To be clear, I am not claiming they stole an idea. They have made significant independent research. However, a specific part regarding the treatment of rotation with bias correction relates to prior work, and it would be appropriate to have that recognized.

That's rationalizing like crazy. If they knew about it they should have cited it.

Doesn't matter, you should still cite. It's basic manners in science.

The earlier paper was from 2021!

> But if they read your paper enough that they invited you to a talk, that probably means they were far enough along to independently inventing it

That's more than a stretch. They likely invited them because someone thought the abstract sounded interesting, or something like that.