Dude if he revealed that he was human it would be quite possible for him to still be killed or experimented on if not killed, he also doesn't know if the vice commander would let him live or not, since the vice commander may not be friendly towards him and if he was distracted for even a few movements he could've died ( also no one would believe a kaiju could be a good person, if lions could speak and one told you not to fight it, since it was a good person and you were about to kill it would you believe it? Even I can answer this for you,it would be a resounding no,why since it could be lying) . In the end it would be best for him to focus on escape considering all the possible actions he could've taken.