The Giant Pacific Octopus wrote:
Slowly swimming home after winning a fight is running away?
Besides Kong is the star and hero of the picture. You don't have the top billing star and hero retreat from the second billing co-star and villain.
Godzilla was the bad guy out to destroy Japan and was destined to lose. Just like he loses to Mothra's offspring in the next film.
As well the guys who created Godzilla were big fans of Kong. Eiji Tsuburaya couldn't wait to work on this film because he was such a fan of Kong.
And yeah Toho stated Kong won the fight on pages 8-9 of their 1962/63 company book Toho Films Vol.8
Maybe KK and Godzilla cut a secret deal while underwater.

Godzilla: Get the f*(k outta here, go back to that gay island where everyone kisses your a$$ and leave me to crunch Tokyo in peace and I won't kill you and we can forgot it all happened, you big, flea-bitten skunk ape.

I kid, of course. Honestly, yeah, which monster appears before the "vs." is generally the one who wins. Godzilla was on sort of a weird, illogical losing streak at that point. He lost to a giant ape who didn't even have any special weapon and two baby insects. Maybe he went "straight" from Ghidorah on because he figured he would "win" more as a good guy.