I agree the OP's analysis itself is a bit shallow, but I don't see how that can be related. If you embed a video and do not do anything with its output then WebGL is simply unrelated. In fact most of websites in question do not seem to use WebGL visibly. That fact combined with a direct check for WEBGL_debug_renderer_info and so on should flag a suspicion. Explicit alternative explanations would be needed to prove innocence.
So that's how they're related.
And let's not assume guilt and then require proving innocence? It works the other way around. It's the burden of the person making the accusation to form a strong case. Which is not done here at all.
I still believe that the presumption of innocence should not apply in this case, because fingerprinting is already close to guilty (if you don't agree to this premise there is no point for further discussion, so please refrain from arguing against this specific point). You are right that feature detection is not fingerprinting but they are virtually indistinguishable; given how widespread fingerprinting has been, it was enough to suspect so.
You could take literally any line of code and make an unfounded claim. "It calculates a hash, and fingerprints use hashes!" "It stores a variable, and analytics uses variables!"
It's on the burden of the person making an accusation of bad behavior to actually demonstrate that. Otherwise it's no different from me declaring you're an evil hacker because you comment on Hacker News, guilty until proven innocent.
The null hypothesis determines the "unfounded claim". For example, judicially, the null hypothesis is, "You are innocent until proven guilty in a court of law." Similarly, commercially, the null hypothesis is, "If it's profitable and mostly legal, corporations will compete to do it better."
Fingerprinting is both profitable and legal. It is so profitable and so legal that today's most dominant corporations, entities representing trillions of dollars of value, are founded on its premise.
The "unfounded claim", therefore, is yours. Or do you have any evidence that you are not being surveilled?
There is zero evidence any of these are being used for fingerprinting, which is defined as building up an entire set of capabilities to uniquely identify a user.
Essentially all of these seem to be attempting to identify the graphics card, and all of these could be related to feature detection for an embedded video player, for example. Feature detection is not fingerprinting.
Fingerprinting is pretty easy to confirm, because it collects a large combination of data points (fonts installed, canvas rendering quirks, etc.) and either reports or hashes them all together. (That doesn't mean it's easy to find the code that does the fingerprinting, but once you've found it it's quite obvious what it's doing.)
It is deeply irresponsible and misleading of the author to claim fingerprinting without looking for that type of combination. And slapping "No claims made about accuracy" at the top of the page isn't an excuse.