That distinction might be interesting if you're defining systemic racism but otherwise racism is having preconceived notions about a group, or attributing qualities and flaws to a group, based on race. That's exactly what the author of that post is doing, lumping all whites people in a single group, ignoring their multitude of opinions and experiences.

No. The author of that post is denouncing systematic racism and as such the domination of white people over minorities. That’s why they must talk about white people as a whole.