Vegeta always gains a power up when he enrages, like all other sayians actually. Seeing bulma being hit made him enrage and his rage fueled his power so he bekame much stronger than SS3 goku for a brief moment. This used to happen with Gohan before he got his potential unlocked like 7 times... gohan is a pussy as he didn't keep on training since cell games so it seems fit that he's weak. Also Goku was able to hold out against Bils after reverting from super sayian god because he's a fucking genius and kept some of that power even in his normal form. Bils states that after experiencing that power(of god) it remained with him even after the actual transformation wore out even if it wasn't full power if you watch it with proper subs. so yeah I'd say watch it with proper subs if you wanna understand the plot .