1. He could have when you weren't watching/. 2. What? 3. Because he'd never seen it before in his life. 4. No.
1) He's been accounted for whenever he wasn't on screen
2) Them's the rules kid.
3) He's never been to this red sun planet
4) Go stick your dick in a vat of acid.
Hahahaha... Goku has lived long after Omega Shenron was defeated. He was taken in by Shenron to an unkown dimension to train. I'm pretty sure he's aware of some red sun galaxies or planets that are there.
No feats, therefore irrelevent.