Nice question!

Who knows what sort of Mitzvah or Mitzvos Rabah bar bar Chanah was occupied with when the coach arrived. More likely still, he was engrossed in a Sugya. Many stories are told even of modern Gedolim who were so engrossed in their learning that they forgot to eat. R. Shach z.t.l. was known to bump into lamp-posts as he walked along the street engrossed in a Seifer, and to apologize and walk on.

R. Chiya berated Rav for asking Rebbi a question in a Sugya that was in a different Masechta than he was currently learning, because he might not have been able to answer it. I have no problem with answering from one Masechta to another. Do you?

It seems that we do not know what it means to be fully preoccupied with a Sugya to the extent that nothing else in the world exists, making it extremely difficult to come down to earth.

The great thing about Rabah bar bar Chanah was that he remembered in time and then did the correct thing, as the Gemara explains. Because at the end of the day, Tzadikim are governed by Halachah, and receive Divine assistance in carrying it out. And that is what is important.

Rav Eliezer Chrysler