I found a strange bug in my game, as I visited this strange planet that has two stars of type F (white stars), but on this gazeous planet it reveals that it is orbiting a star both. There is a red reflection on the gaseous planet. Where as the system has no red star of type M.

Unfortunately I don't have that system in my program, probably because you have some mod for adding galaxies or something similar, so I can't verify.

It's the moon.  The first one to be exact.  It's hot enough to light up the gas giant with a dull red glow.