The parent didn't justify anything.
https://en.wikipedia.org/wiki/Whataboutism#Methods:
> "[Whataboutism] functions as a diversionary tactic to distract the opponent from their original criticism. Thus, the technique is used to avoid directly refuting or disproving the opponent's initial argument."
for example, ad hominem is not a "logical fallacy" unless it is used in some kind of logical construct (such as a syllogism). it's not necessarily a "logical fallacy" to just simply insult someone in some subjective or qualitative way.