Here's a question I missed from Hamachisn't:
"Why does Chax think the station was protecting Aun alone from the foe? Was not Chax in equal danger?"
Aun seems to have been the target of the attack by the "Nocturnal Migration," as he attacked them when they scared him out of sleep. Chax did eat of the flesh that Aun cut off, but this probably went unperceived by the N.M.
Additionally, Aun feels that he's being called by something to investigate deeper. This 'call' took the form of a rumbling noise from the ground. Aun and Chax don't know yet what the source is, but the chances are fair that it's some part of the station.
Chax does not perceive this call directly - it's not his fight, though he has volunteered to aid Aun.
Taking all these things together led Chax to assume that the station is more concerned about Aun's fate than Chax's.