Ok this is hard to explain, i had a piece of my pickup come out on my ibanez rg5ex1 i have no idea whats its called lol i will just call it the dot. It looks like it was just glued in by the residue i could see on it but i dont know if it was or if it was put in some other way its the only one that will come and and it is threaded
The part that fell out is one of the pole pieces from your pickup.
It should be magnetic.
You said it looks like it should thread in. Did you try? That's what I'd attempt first.
Normally, pickups are "potted" or sealed in wax or a similar material. It stops vibrations inside the pickup.
Perhaps that's what you identified as glue?
Here's a bit of information about pickups in general, and humbuckers in particular. There's a paragraph in this page that talks about adjusting your pole pieces. It's not a necessary thing to do, but it might help you understand what's going on when you re-install yours.
I wrapped a newspaper ’round my head
So I looked like I was deep
