It was a surprise to many, myself included, for sure, but without interviewing the people able to vote, we can only speculate.
I think that, frankly, having a live Foley artist, while impressive, does not necessarily equal great design. It's the same argument of "most sets" or "most costumes" versus "best set" and "best costumes."
The design awards also tend to be most likely to be caught up in a sweep.
"...everyone finally shut up, and the audience could enjoy the beginning of the Anatevka Pogram in peace."