Is it possible for a SLW to have a single comb? As far as I've heard they only have cushion combs.
Yes, it can happen. Rose comb is dominant to single comb, and sometimes the single comb will pop up in rose comb breeds.
But the spangled breast and wrong colored legs rule out a pure Wyandotte. He may or may not have some Wyandotte in his ancestry.
He sure is pretty, though.