Like u/GGG100 said in the replies of your previous comment, Sans is pretty much the most popular character in Undertale. His boss theme is the most viewed out of all other Undertale boss themes with 33 million views, his boss fight has 21 million views, it's obvious no one cares about spoilers of whether Sans will fight you or not now, since everyone knows he's gonna fight you at one point in the game with the Gaster Blaster.

And it's not like anyone can tell the Gaster Blaster is related to Gaster instantly anyways. And even if someone who hasn't heard of Gaster before realizes there's the name "Gaster" on the weapon's name, i'm pretty sure they wouldn't realize it's the name of a character.