Good try, but your premise is based on strawman. Their logic is flawed, but not because it is actually flawed, rather you think it is flawed, therefore you fail to see the logic in the argument. Know thyself, said Socrates who sought knowledge and perspective. Know thy enemy, said Sun Tzu who wanted to learn from his enemy's mistakes in order to prevent his own.
Microaggressions are not an extension of systemic racism but a product of them. However, not all passive aggressive comments are motivated by racial, sexist, or other biases. If not all passive aggressive comments are not motivated by biases, then one can assume that not all assault is racially motivated. If one were to assume everyone who has assaulted someone was due to race, you'd find most assault takes place between same-race, even same-sex people rather than people of different race and sex. So, we cannot assume in this incident that because he is white, and she is black, that he assaulted her for this reason. Unless we know what was exchanged or what lead into this, you can assume that race was a motivation just as easily as one can assume sex was a motivation. Or what kind of politics they represent.... until we know, we don't.
Systemic racism is not a classification of individual racist action, but a group of them. When more black people are arrested than white people, or viceversa; that is an example of systemic racism. When more black people are shot by white cops than black cops, that's evidence of systemic racism. When more white people are gunned down by cops than black people... that too can be evidence of systemic racism.
The incident above may be individually be racially motivated but it's not statistically valid as very few white people attack black people, especially strangers.
I actually have that data here...
https://bjs.ojp.gov/content/pub/pdf/htus8008.pdf
Granted, it's old, but I failed to find a more contemporary data that was as widely encompassing. Still, without a wider pool of incidents, it cannot be determined a systemic racism. Racism? Maybe! But not systemic.
As I said, good try, but no.