If you think about this event in a vacuum, maybe it makes sense to argue, "Well, it could be age and not race."
He's right that we can't know whether racism was what motivated the store manager to follow these teens around the store - but that's true about every single incident when this happens. At some point you have to observe the larger societal context, note the fact that the black (male, especially) experience of being stalked around stores is nigh ubiquitous, and conclude that, yes, it probably is a reasonable position to think that racism was key here. It's certainly not a wild-eyed and irresponsible position to take.
But I'll think about reading the book, Dookkake.