he didn't know at that time that it was his tendon, not the bicep muscle.
pretty amazing. but with his strength, its not surprising he could compensate with the rest of his body. but it is surprising he could right after it happened.
i'll bet he couldn't have done a bicep curl. not much of one anyway
and there wasnt really any risk of him damaging this further. it was snapped. but he could have done damage by compensating with other muscles and straining them however.
“You can discover more about a person in an hour of play than in a year of conversation” – Plato