Experience

History

A person trying to learn doesn’t constantly disagree/contradict you and never express that their understanding has improved. A person sealioning always finds a reason to erode whatever you say with every response. At some point they need to nod or at least agree with something except in the most extreme cases.

It also doesn’t help their case that they somehow have a such a starkly contradictory opinion on something they ostensibly don’t know anything/are legitimately asking questions about. They should ask a question or two and then just listen.

It’s just one of those things that falls under “I know it when I see it.”