HE can be tricky stuff to diagnose, from what I understand. It’s quite possible to have significantly elevated
levels of
ammonia and not present with HE, and conversely to have very low levels and significant HE. My understanding is that while ammonia isn’t always diagnostic for problems it is associated with them.
He might want to reduce animal proteins for the short term, just in case. It won’t hurt to exchange red meat for legumes for the interim, until he can be seen, eh?