I don’t know what ‘sealioning’ is supposed to be, but in practice the main purpose of such an accusation appears to be to excuse personal attacks on someone you are debating with. Under this framework, attacking the argument rather than the arguer is recast as a bad and sinister move, and cruel personal attacks are justified as the deserved response. Quite impressive that they have managed to turn being polite into a bad thing, but that is a necessity when you can’t win on the merits.
Imagine the sealion in the original comic as a disabled person, and you’ll understand.