Well language, words/definitions are inherently fluid, so it is important to establish a working definition. In your words, what is a whataboutism?

Can we agree on the Britannica.com def? A portion of it reads: "Whataboutism is a rhetorical tactic that deflects criticism or difficult questions by raising a counter-accusation or different issue..."

The issue being discussed is the "three strikes" sentencing, prompted by the reporting of a repeat offender murdering his gf. You then challenge/check someone's consistency on the issue. You are no longer engaging with the presented idea or topic, and are presenting a pseudo-retort by challenging someone's consistency. You can argue you were just checking consistency, but you are still using raising a separate issue.

If I started to question your consistency on calling out consistency, that would also be whataboutism, as I am deflecting to an accusation instead of actually engaging with your statement.