After the ruckus with Error, the question was safety of other AU's. Now Ink could've went himself, but does Dream trust him not to get distracted? Absolutely not. And does he want to leave Swap alone? Absolutely not. So all 3 went thru AU's to, well, check on them. Most of them were similar, Sans usually found them at the 'gate' after Ruins, and they kinda just went thru with it as usual. Nothing new

So now they're in your AU, with Ink beaming to check thru this, probably grab a snack, and move onto the next AU as they stand at the 'gate', hearing the footsteps behind them