Why would Goku got stronger after Tamborine knocked him out?
1. Roshi states that even young, neither he nor Mutaito could combat Piccolo in order to stress the situation, implying that Mutaito > Prime Roshi > 22nd TB Goku. Piccolo Daimao later finds it an impossibility that a human could kill one of the Mazoku, implying Goku's strength after recovering is at the top of this chain. Since Daimao did only mention a human of "this era", it could easily just be that he didn't expect there to be anyone close to Tambourine's level, hence why I only bring up such as a possibility.
2. There's also Kuririn's statement in the Namek Arc of Goku getting stronger after each tough fight as a result of Zenkais. If the events in Muscle Tower were enough to warrant an increase in strength, I'd say falling a great height after being beat up by enough he was knocked unconscious would be enough for this to constitute as a slight Zenkai moment for Goku.