It's claimed Steve played the hook on a Minimoog, but there a body of synth experts who swear it's a Micromoog.
On top of that, Steve is playing what looks to be a Polymoog in the video.
Yeah, keyboard players get hung up on some weird stuff.

IIRC, Winwood was inspired by several contemporaneous records that were made mostly or entirely by massive overdubbing, with few or no outside collaborators: Prince, Stevie Wonder, Gary Wright, etc. Winwood's Arc of a Diver was made in his home studio, and he did much of the engineering on the record as well as performing. The story goes that Winwood had an entirely different intro (which included drum tracks) recorded for "While You See a Chance" that somehow got deleted from the multitrack master. The intro on the record, which is entirely keyboard-based, was added after the fact.