I agree with the GP on the definition of whataboutism, and think that you have described something with a much older term: "pointing out the hypocrisy".
They both share in common that rather than continuing to talk about just one thing, you are now talking about (at least) two.
But whataboutism is a diversion tactic that tries to shift the attention from behavior/event A to behavior/event B; pointing out the hypocrisy notes the similarities between behaviors/events A and B and contrasts the response.
Both can be deployed in similar situations, but the motivations for choosing one over the other are substantially different.
They both share in common that rather than continuing to talk about just one thing, you are now talking about (at least) two.
But whataboutism is a diversion tactic that tries to shift the attention from behavior/event A to behavior/event B; pointing out the hypocrisy notes the similarities between behaviors/events A and B and contrasts the response.
Both can be deployed in similar situations, but the motivations for choosing one over the other are substantially different.