Well, this theory is becoming a little bit more believable, but there's still one thing that bothers me.
Goku just didn't seem injured enough to get a zenkai. Let's look at everyone else.
Vegeta (Sayajin Saga): Hardly needs an explanation.
Goku (Sayajin Saga): Like Vegeta, hardly needs an explanation.
Vegeta (Namek Saga): Vegeta's face looked like lunch, and overall, he didn't look much better than his Sayajin Saga self.
Vegeta (Ginyu Saga): This one causes a lot of controversy, yet he was more injured than his Sayajin Saga self (BEFORE HE GOT CRUSHED BY GOHAN), and that Vegeta said that he needed medical attention, meaning that he was really badly injured. Keep in mind that that Vegeta could still punch Krillen and Gohan around.
Goku (Ginyu Saga): Not too much better than his Sayajin Saga self.
Goku (Freeza Saga): Needed someone for support and his eyes looked like a drunkard's.
Reference pictures in case you don't believe me:
Android 17 vs Gohan
You see what I'm getting at?