The context of what each speaker is saying matters. Words don't have much meaning in isolation except for simple ones like "no". You could have a degree in the Philosophy of Science and still struggle to define "theory" accurately and succinctly.

One speaker is using the word as a positive thing (accurately). After all, a theory is the best we can say about how the world works. The second speaker is using the word pejoratively. In that sense it actually doesn't mean the same thing, and any scientist would argue that the second person doesn't understand what they mean when scientists say "theory".

Note: I said when scientists say theory. Words don't have inherent meaning, so the speaker matters. The speaker can only hope their audience takes their words the way they're intended. There's no guarantee that they will.

The second speaker is trying to refute science by quoting scientists, yet using the word in a way that scientists don't. That's obviously dumb. But it is the way that most non-scientists use the word, so you could say the second speaker is just confused about what scientists have been saying when they use the word. The scientists' goal should be to correct the second speaker's understanding of what scientists mean when they use the word. The word itself is not actually important. You can get across the meaning without ever using the word itself.

So who's right and who's wrong? Neither. It's a simple misunderstanding of how scientists uses the word when they speak. Unless, of course, the second speaker knows the scientific definition, and is pretending to not know in order to pander to an audience.