Bathroom sink trap questions

Thanks in advance for any advice. I took the sink apart so that I could wainscot over some terrible sponge painted walls. I had no problem taking the J bend off. I couldn't seem to get the wall tube loose. That's when I discovered the wall tube is unlike any set up I've seen while researching on line so far.
The wall tube appears to actually be 2 pieces; a short straight piece and then a small piece that starts to bend [ that would fit to the J bend] that appears to be sweated on to the straight piece. Every video I've seen, the wall pipe is one piece and is inserted into the stub out. This small piece fits over the straight wall tube and appears to be sweated on. What's confusing me is there is also a nut that doesn't seem to be holding anything together between the straight wall tube and the piece that starts to bend because I believe they're sweated on. If you look at the pictures, you can see when the nut is fully tightened, it actually goes over and beyond where they 2 pieces fit together.
Please excuse my ignorance on the subject and thank you

The piece coming out of the wall has a solder bushing attached to it, that will unscrew from the fitting in the wall.

Thank you John. My ultimate goal is to get the wainscoting up, put an escutcheon on, and re attach the J bend. I recently moved into the house and although I didn't use the sink too often, I didn't see any leaks. I'm not looking to make any more work for myself so I don't need to take the wall pipe out for any reason if I don't have to. If you don't mind, does the small piece that begins to bend and attaches to the J bend (3rd picture), does that look like a compression fitting? There was no rubber gasket under the nut and don't know if it needs one. If not, I'm just going to put the wainscoting up, reattach the J bend and put the sink up.

Thanks again

Yes that is a compression fitting.