He was doing the guys night thing, she was doing the girls night thing. One of those guys was dating one of those girls so they all met up. That guy and that girl broke up a few weeks later but, at the bar, Kat and Ben fought about whether or not Big Foot has a tail and, obviously, they were both interested in seeing where this was gonna go.
Halloween is Kat's favorite holiday, so Ben ordered take out from their favorite Indian spot and sprang the question on her in their kitchen before she could even get out of her coat. They excitedly shared a bottle of nice Italian wine, got nauseous from downing the wine on an empty stomach, and watched some Brooklyn 99.