I don't think the question is stupid at all, the answer is just relative. On my end, the answer is a clear YES: I am seeing this on Mastodon, I am responding on Mastodon, I have no obvious way of telling you're not on Mastodon.
If "this" refers to the site you're posting from, the answer is obviously no. If it refers to the site it appears on, the answer depends on the reader.
If the question refers to the platform, I guess it's neither Mastodon or Lemmy, but ActivityPub.
@lookmomnodrugs
Yeah, platform was a bad choice of word. But as the content travels through the protocol, it makes no more sense to say that the platform of this post is Lemmy than it does to say that the platform of an email is Gmail, even if it is received by users on other providers.
The platform in a strict sense is, to a degree, irrelevant. I guess it's platform agnostic. If we had to name one maybe it's the fediverse.
(I'm not sure I even federate without tags, so: @DarkThoughts @lookmomnodrugs )