Rashi on Amud Aleph explains why Rav Zeira was considered among the pious of Bavel, based on two stories about his life.

Bava Metzia (85a) tells us about Rav Zeira:

When Rabbi Zeira ascended from Babylonia to Eretz Yisrael, he fasted one hundred fasts so that he would forget the Babylonian method of studying Gemara, that it would not hinder him from adapting to the unique style of study prevalent in Eretz Yisrael. He fasted an additional one hundred fasts so that Rabbi Elazar ben Pedat would not die during his lifetime, which would have caused the burden of communal matters to fall upon him. As dean of the Torah academy, Rabbi Elazar ben Pedat was in charge of all public affairs, leaving Rabbi Zeira unencumbered to study Torah. Rabbi Zeira fasted an additional one hundred fasts so that the fire of Gehenna should not affect him.

Furthermore: “Every thirty days, he would examine himself to ascertain if he remained on his exalted level. He would ignite an oven, climb in, and sit inside it, and the fire would not affect him. One day, the Sages gave him the evil eye, i.e., they were envious of him, and his legs became singed in the fire. And from then on they referred to him as: The short one with singed legs.”

According to Rashi, these two stories are the reason why Rav Zeira was considered among the pious of Bavel.

There is another story of Rav Zeira from Eruvin (28b) that I think may be related:

“Rabbi Zeira was exhausted from his studies. He would go and sit at the entrance to the academy of Rav Yehuda bar Ami, and say: When the Sages go in and out, I shall stand up before them and receive reward for honoring them, as it is a mitzvah to honor Torah scholars. Too tired to engage in actual Torah study, he sought a way to rest while fulfilling a different mitzvah at the same time.”

I wonder what was causing Rav Zeira to be exhausted. I have two possible answers that relate to the two prior stories. Perhaps, after his legs were singed, he suffered some weakness, whether emotional or physical. If that is the reason, it is even more significant that he set out to honor Torah scholars during this weakness. After all, it was their evil eye that caused the mishap in the first place. In that case, it was extraordinary that he showed them, so to speak, no hard feelings. The other possible cause for his weakness could be his excessive fasting. If so, he might have been blaming himself, holding himself slightly responsible for being careless with his health, leading to a loss of ability to study. If so, he specifically sought out to honor Torah scholars to achieve penance. Or, the whole reason he fasted in the first place was so that he would be able to shed preconceived notions and bias from his prior studies in Bavel. He may have thought that while it was a noble and worthy goal, there was a degree of irreverence and disrespect in disregarding what he had studied earlier, and his punishment was becoming weak. In that case, perhaps he sought to honor the Torah scholars as a penance for the disrespect.