A fish that has been hooked on the outside of the mouth, and the hook is facing inward at the hinge indicates foul hooking.
This is particularly the case if that hook has penetrated in the opposite side from where the angler is standing.
That indicates lining or flossing. Same goes for fly fishers.
The hook should originate from the inside of the mouth with the point facing out, or completely inside. It's still possible the fish did not bite, but it's alot more probable that it did bite.
That is what sportfishing is all about, letting those fish go that do not want to play.
It's all pretty cut and dry to me... It's not sporting to keep foul hooked fish. Nor is it legal.
Cheers,
Nicole