Before, you had to tamper with your files to find the character people believe to be Gaster or evidence associated with him. Now there’s apparently an extremely slight chance that his room will appear at a specific point in the game sans tampering. So basically, if all of this is true/intentional, Gaster (or whoever this character is) is canon now. Perhaps it was always intended to be that way, or perhaps this is Fox’s way of throwing a bone to an extremely specific, tirelessly ardent part of Undertale’s fandom.
Haha, that’s funny. Like there are parts of Undertale fandom that aren’t tirelessly ardent! Or you know, that might just be me living with Faith, the obsessed autistic girl.
(Also “sans” and “bone.” ISWYDT.)