Alright, so I don't know if anyone else has pointed this out yet, but you know how Onionsan mentions in chapter 2 that they've been hearing a strange song at night coming from deep under water that they remember from somewhere, but can't quite place?
And you know how there are those mysterious strings hidden in the code of chapter 1 and 2 where it's implied that someone is trapped somewhere "dark" all alone? And how some people have pointed out that the way this person speaks sounds a lot like Asriel, on top of having some parallels to Flowey waking up without his soul in Undertale?
Here's a theory: the world of Deltarune is a construct, there is nothing outside of Hometown, and the song Onionsan is hearing is actually coming from the void outside of the game world. The song is "Memory", the melody the music box plays in Waterfall in Undertale. The music box which, in merchandise, has been confirmed to actually be the same object as Asriel and Chara's friendship lockets. Onionsan is remembering the song because in their other life in Undertale, they lived in Waterfall, and probably heard it from a few screens away.
(It's also worth noting that in chapter 1, if you name Onionsan "Asriel II", they will specifically note that the name sounds like a "memory" ...)
Asriel isn't really at college. He's being stored in the game's code until it's time for him to come visit his family in Hometown later in the game. In chapter 1 and 2, he's in the void beyond the game world by himself, playing the song in the locket to comfort himself.
The voice he mentions hearing in the strings in chapter 2 is either coming from Gaster, who also seems to be trapped in the void - or maybe Spamton and Kris, as this may be Asriel speaking through Spamton in this bit of dialogue:
Also note that the phone in the back is ringing, as if someone is trying to contact the characters while they're talking. We know for almost certain that Spamton used to communicate with Gaster by phone, so there may still be some sort of connection between him and the void where Asriel is now trapped until further notice, allowing for contact even though phones in the Dark World normally only pick up the "garbage noise" also associated with Gaster.
What implications this has for the wider scope of Deltarune, its world, Gaster's storyline and possible connections to Undertale is a mystery, but 1 thing is for sure: poor Azzy's never getting that damn degree
