Longboarding has it's similarities but is quite different in my opinion.
I've been a long time longboarder and I've snowboarded a couple of times, and I remember watching a video of some people doings standies and thought "Wow that looks so much like snowboarding". Still, I feel like almost nothing transferred over from longboarding at all. I mean, I have better balance than a beginner snowboarder, but that was about it. I struggled the first hour or two because it was just so different to me. The whole concept of riding on rails and being strapped into the board felt restrictive.
In longboarding, standup slides are an acquired skill that takes a lot of practice. In snowboarding, it's probably the first thing you learn, and probably by accident.