Undertale - Sans’s secret

Getting Sans to show us his room and his secret lab. I triggered this event through 2 seperate pacifist runs, the first one not shown on the video, but I believe it might be possible to trigger this by talking to Sans once, reloading before meeting Sans in the hallway, then talking to him again. I’m not 100%, so I’ll prolly check next time I play the game, but if someone could validate, that’d be swell :) Also I’ve seen some comments online stating this is only possible if you’ve never sold your soul at