Sans in deltarune might be from undertale, what I'm referring to by "from undertale" is a complete genocide route, when you supposedly "kill" sans in a genocide route, it makes a spare noise, but you'd ask "how does the LV go up?" and to that, I don't know, but if you check stats after "killing" sans you'd see that the kill count hasn't gone up, meaning sans fled, he probably counts dead in that world and the damage dissappeared due to him suddenly being in another world, a place he can call home, a hometown perhaps?