Whataboutism isn’t excusing; it’s deflecting. To quote from the OED:
“The technique or practice of responding to an accusation or difficult question by making a counter-accusation or raising a different issue”
While whataboutism is definitey toxic to conversation, I've noticed a lot people tend to throw accusations of whataboutism around when they are uncomfortable with their hypocrisy being pointed out.
This is exactly what you’ve done.