Kovarex' message for which he is accused of sexism is just pedantry about the definition of "bigot".
Given that all this is taken from a huge endless discussion of that post, picking out a weird pointless bit of pedantry not addressing the original baseless accusation and calling that "proof" is a major stretch. (also the original accusation it isn't even shown, only paraphrased, which is weird)

I don't see the accusation of sexism having any footing at all if that is all of the "proof".

The homophobia part is mixed. I think Kovarex did fall for the right-wing projection that homophobia is "pushed into" media, and that you will be cancelled on twitter or smtn if you don't watch it.
Kovarex did however agree that if someone hates gay people, they are a bigot, and hating that homophobe in turn does not make you a bigot.

I don't think Kovarex is homophobic, he just fell for some weird right-wing talking points about popular media and twitter mobs. (Also this was 3 years ago, he might well have realized the mistake since then)

The racism is completely unfounded. I assume this is derived from the first part which seeks to apply guilt by association. FFF #366 quoted "uncle bob" who is described as "a racist, sexist and Trump supporter" by the accuser. I don't think it matters so I will simply assume it is true for this matter.
Kovarex' point is simply that quoting good advice is independent of who it came from. Saying "If Stalin had a good writeup on programming" that would not matter. He would quote it if it was good.
I don't fully agree, quoting someone extensively like that does push people towards them, what I have seen done before is a simple disclaimer that "the person holds weird views so don't mind finding that mixed in with their advice if you look them up", something along those lines.
What I do not at all agree with is that it makes kovarex a racist or sexist.

Guilt by association is a fallacy with its own wikipedia article, I consider the racism point dead in the water if that is it. I also consider the entire source extremely suspect for including that.

Finally, the rape part. I think this holds the most water out of the claims. I will quote it in full first:

• The male teacher preys upon and rapes the female student.
• The female teacher seduces and has sex with the male student.

It's statutory rape regardless of the genitals attached to the adult in the situation.

kovarex:
"statutory rape"? A new sjw term?

Yeah lol. Those darn two and half century old terms really scream "sjw" don't they? /s

kovarex:
I always thought, that rape means that you assault someone against his will. If teacher seduces his/her student and the act is voluntary, we can't really talk about rape right?

First of, this is 6 years old now. Also I cannot find it anywhere, the only source is the screenshot in the linked page.
Now to me there are two main interpretations here. One is that the question is legitimate, the other being that the question is rhetorical. If it was rhetorical, I don't understand the first question. Calling "statutory rape" and "sjw term" does not hold any arguments or dog whistles, it simply makes you look like you don't know anything about this topic. Which is what I think is the case here. Kovarex has no idea what that term means, or really about the complexities of rape in a legal and moral sense.

Assuming then that the second question is legitimate, I think it is fair to ask. In a colloquial sense in the ancient before times, rape meant something violent (probably, I'm not old).
Ofc then we were enlightened that you could be threatened, or drugged. And at that point it shifted to being consent-based. And if you then add an age or power hierarchy element, you also disqualify certain people from consenting.
At the end of that you hopefully come to the conclusion that calling it all some form of rape is sensible.
Either case, lawmakers generally have done that, and the resulting legal definition I assume is called statutory rape and might confuse someone hearing about that for the first time.

I assume therefore Kovarex simply had no idea and learned a new thing there.
Immediately jumping to "swj term" does again remind me of the riling up that right-wing influencers do. If you are told constantly that "sjw" are inventing new words and pushing xyz into media then you do jump to that for every normal thing instead of thinking about it more reasonably.
To me it sounds like Kovarex was in the "alt right pipeline" at the time. I can't speak about their opinions nowadays, but given the article doesn't have anything else I have no reason to believe Kovarex followed through and somehow became a radical right-winger since.