Wow, those are nice! The ones I'm making are nowhere near that complex, it's a very basic pattern for beginners.
Did you create that pattern?
Yep, but it's mostly a mitten pattern, except I didn't close the thumb. Easier to make than a sock.
Mostly, I cast on 48, k1p1 for the length of the arm, added 4 stitches for the base of the hand, knitted in pattern to it was time to do the thumb gussets, made sure the thumb gussets stayed in pattern,knitted the thumb long enough, went back and knitted the hand long enough.
What's handy is to find a mitten pattern you like, and use it as a guide. Just don't close the thumb or the top.