I don't think it's completely true to say it's not accurate in any way. You can still get a rough estimate based on the proportion of likes to dislikes coming from people with the extension installed, then extrapolate that out based on the public number of likes provided by YouTube.

Of course it's not going to be anything more than a ballpark number, but being able to tell the difference between "almost nobody is disliking this" and "like half of viewers are disliking this" is super useful information. If nothing else it serves as a third party keeping a dislike count for users who installed the extension. They're not claiming to access the real YouTube data, so I think it's unnecessarily dismissive of what it does to call it bullshit.