Cherrybim,
It does not mean that they don’t trust their Rav. It means their minhag is not to eat out the house on Pesach.
I heard the following directly from the person in the story.
He was a talmid of Rav Pam. He and other talmidim went to Rav Pam on pesach. He was offered something to eat, which he declined because his minhag was to not mish. He started getting ribbed for not eating in Rav Pam’s house. Rav Pam told the person to not chepper this bochur, his minhag is legitimate. He also offered a reason, that not eating chametz on pesach requires Mazel, your own Mazel you have no choice but to rely on, but why do you have to rely on other’s Mazel.