There were four lotteries performed in the Temple every day that established which of the kohanim would perform each part of the sacrificial service. The first Mishna in the perek describes how the appointed kohen would perform this lottery and charge the kohanim to look to the east to watch for sunrise, which would allow for the beginning of the daily service in the Temple.
Upon sighting the sun, the kohen would shout “Barkai (There is light)!” The Mishna continues by quoting Matya ben Shmuel who says that another question followed – “Is the entire sky illuminated as far as Ḥevron?” This was necessary because of an error that had been made once, when the light from the moon fooled the kohanim and they began the avoda before the appropriate time, and the korban tamid (the first sacrifice of the day) had to be destroyed.
There are different opinions about the statement made by Matya ben Shmuel. According to the Rambam, Matya ben Shmuel was one of the tanna’im, and he was disagreeing with the first position in the Mishna, arguing that the question presented in order to clarify that sunrise had occurred was whether it was light in the east all the way to Ḥevron. Tosafot Yeshanim argues that Matya ben Shmuel was the name of the kohen who was responsible for the lotteries that were done in the Temple (his name is mentioned in that context in Massekhet Shekalim). If we accept this explanation, then he is not arguing, rather the Mishna is describing that after the first sighting of the sun, Matya ben Shmuel followed by asking whether it was light all the way to Ḥevron.
The Meiri explains that Matya ben Shmuel’s question was whether the kohen watching for the sun could see all the way to Ḥevron in the south. In any case, the Jerusalem Talmud points out that everyone agrees that the reference was specifically to Ḥevron because they wanted to invoke the city where the forefathers of the Jewish people are buried.