I recently got my braces tightened two days ago and for some reason one part of my gum became red and puffy and i dont know why?

Ortho adjustment: See your Orthodontist for an evaluation. Could be many things- accidental irritation which will go away on its own or something that needs to be addressed by your Orthodontist.

Return to dentist: many possibilities, but visual inspection will determine cause

Inflammation: Can be from space closure, draped food between teeth, area that is not being flossed, a localized gum infection, an abscessed tooth, or many other reasons. Return to your treating Dentist or specialist Orthodontist for determination of the cause and appropriate care.