it could be a type of fisherman’s rib. (the half version, maybe?)
here is a pic of the half-version of fisherman’s:
it may just be a matter of yarn and needle ratio to make it look so bulky.
I just knit a hat in a really chunky yarn that came out looking alike to what you want… I may be able to take a picture tonight. I made mine by fisherman’s with working all purls and knitting all knits in the row below. really easy, quick, elastic fabric and almost that look.
the other option is what I am just making in a baby blanket. Looks similar, too and comes close to the pic I found above:
I mean square 2 and pattern M2 in that blanket there - that would give you the explanation. It turns out a wonderful deep rib, very puffy, elastic, VERY nice for a blanket, since it will be very warm.