After he calmed down, Aru spent the rest of the night explaining to Nom how he survived the harsh conditions of the Valley of Death. However, he made sure to avoid anything related to Airavat and his temple in his explanation.
No, it wasn't because he thought Nom was untrustworthy. According to Aru, if there are people he could trust, Nom would be at the top of the list.
Still, he hid the information about the temple to prevent any unnecessary complications.
For example, the trust Aru had for Nom doesn't transfer by default to the people that Nom trusted.
So, if Nom were to unknowingly mention it to someone he trusted and that person leaked the information, it would do more harm than good to all the people who knew about it. After all, the spirit of a Divine beast and the temple inside would surely attract the attention of the greedy.