He said he was doing that because Tenshinhan was trying to kill him, not because Tenshinhan had been stomping him. If you're dead even with an opponent who's trying to kill you, obviously you won't take any chances if you have access to another level of power.
And? Goku said the only reason he held back his battle level was to avoid killing his opponents; when that limiter was broken (something Goku did as a counter to Ten's killing intent; he even said "Ora mo sentou you no pawa de yaru!" in the original which means
I'll use my battle-purpose power, too!), it was fair game. And again, nobody noted Ten's performance was suddenly far better when Goku unleashed his FP; Ten was relatively the same in performance throughout the match, and was straightforwardly outmatched by FP Goku.
I think Crane Hermit would have done that anyway, unless he was sure Tenshinhan had a big advantage and could win with no problems.
Ten was on the losing end because he was inferior in power and technique.
