Yeah, sure you can argue that the cop murdered George Floyd for reasons other than race. Although race probably was a pretty significant factor. Even if it can't be proven how events would have unfolded had he been white it's certainly fair to assume it would have went differently.
Although at the end of the day, does it even really matter? Police shouldn't be killing people like that full stop.
Didn't say otherwise. But the protests are specific to the black population, not in general. It's a specific grievance and there's an assumption that it applies here.
Though, again, why do you assume that it was probably a significant factor? Where does that assumption come from outside of your own prejudices?
Well while it may only be based on opinion until the cop actually comes out and says so (assuming he's telling the truth) the long history of racial tension certainly does lend credence to the idea that it was motivated by race.