TB, don't forget that by that scene Tom had already been removed as Consigliere. That, combined with his generally taciturn disposition (as I characterized him above)would account for a perceived displeasure with Moe. Remember also that in response to Fredo's appeal to him to intervene with the Don on Moe's behalf, that he rather irritatingly tells Fredo that Mike is in charge of the family business. Tom was already in a disgruntled mood.