I thought that might be the case as well, esp due to the camera focusing intently on Caleb's face after the second save. But the part where he leaves all his gear behind just didn't make enough sense to me. Perhaps he didn't want to face Ann again? But still, there are 3 known survivors and 1 just up and leaves with only the limited-use biosuit? Seems unlikely but possibly just an issue of suspended disbelief that the director assumed most would either not notice or not care. As an aside: I did not read the book. If there are other clues there that lead to your point then it might make more sense.