about the smicha process- what kind of 'rav' would have the title,but be nechshad as an am haaretz-meaning not knowledgale of th e gmara process. It makes one wonder what the requirements must have been. and even if it means he didn't participate but just knew the maskana, didn't a 'rav have an implication of today-to be able to give psak: neccesitating an ability to be mdayek from the halachot pukot? kol tuv
Rami Bar Chama did not know that Rav Menashya was a Talmid Chacham, as the Gemara concludes, and therefore he refused to include him in a Zimun. As to your question -- how could Rami Bar Chama be mistaken -- after all, Rav Menashya was referred to as "Rav" -- the answer is that in Bavel, there was no Semichah. The Sages in Bavel were referred to as "Rav" out of respect, while the Sages in Israel were referred to as "Rebbi" because they received Semichah (see Sefer ha'Aruch, "Abaye"). Therefore, being called "Rav" was no indication that a person was a Rav. It could be that Rav Menashya was not called "Rav" at that time, or that Rami Bar Chama did not know that he was referred to with such respect just as he did not know that he was a Talmid Chacham (or perhaps he assumed that Rav Menashya earned the respectful title for some other reason, such as by virtue of his age or wealth).
All the best,
Yisroel Shaw