Yes, the knee is and was a gesture of anti-racism. That's why they are doing it. They say it's not political and I believe them.
For me, anti-racism connotations are a little different to anti-semitic connotations, such as those of the quenelle or a Nazi salute. One is positive and inclusive, the other is negative and exclusionary. I mean, racists are going to be riled up by any gesture they perceive to be anti-racist aren't they? In the same way I would probably boo a Nazi salute. I have no qualms in saying what I believe is right and that the motivation for taking a knee is generally positive whereas the motivation for making a Nazi salute is generally negative.
I think you simply want to ignore the wider context of the gesture because it doesn't fit with your idealised view of what was happening.
For you, if someone says something isn't political, that's enough for it to not be political - as long as what they're doing is "positive". Which is a strong indicator of subject bias in my eyes.
To me, that approach is dangerous, as it allows something to be a shield that is beyond reproach that opens avenues for some very nasty things behind it.