Warlock has to sell their soul to a diety. Paladins basically do the same thing but they're jocks for god. Whenever playing as a magic user, it usually comes down to where their powers come from.
Some worship, some sell their souls, some just learn through books, some are born with inate magical abilities, etc...
I saw it more as a dig at the whole loli versus lalafell thing, where fans of the former always seem to disguise their intent behind the convenient happenstance of the latter.
I interpreted this as Sans thinking the sorcerer is Dumbledore, who did indeed manipulated children for his own goals, but it turns out it's Gandalf, so it's a little bonus joke.