That would explain it. Somebody traded me the itch key on groupees (it didn't include a steam key). For some games you redeem the itch key and then get the steam key from the itch download page, but I guess this isn't one of those.
Yea then you don't have access to Steam key. But here on Itch i upload newest version of the game so you can make decision about purchasing it later on Steam with discount for example :) Or you can ask your seller.