This is not whataboutism, because it's all related to the same line of logic.
Whataboutism is when you call up a completely different issue to try and derail the conversation. "Donald Trump has been accused of molesting goats on six different occasions? Well, what about the time when Obama wore a tan suit? Shouldn't that get scorn too?"
Not so. His post is a valid argument, because he is pointing out errors in the Republicans' own logic. Specifically, the Republicans' attempt to ram through a nomination without proper oversight because of a looming election is incongruous with the justification they used during the last election cycle, which is that "judges should not be selected within a year of an election".
The Republicans in 2016 established that it was OK to slow-walk a nomination if an election was coming up, ergo the Democrats doing the same in 2018 is fair play. You can like both or hate both, but pointing out the logical inconsistency in the Republican position is not, in and of itself, a logical inconsistency.
How is this any different from the numerous whatabout responses in reference to bringing up Obama's massive deportation that the left turned a blind eye to while blasting trump for the same thing? It doesn't matter how you try to frame it. It's textbook whataboutism