How could a Levi be from the family of Yehudah?
Rashi: He was a Levi from his mother's side. 1
Rashi citing Bava Basra 109b: Because he did like the actions of [the evil king] Menasheh, who came from Yehudah, he is called from Yehudah's family. He was a Levi, the son of Gershom ben Moshe Rabbeinu, like it says below (18:30) "v'Yehonason ben Gershom [ben Menasheh]." Refer to 18:30:1:1 and the note there.
Radak: It says Beis Lechem Yehudah because there was another Beis Lechem. "Mi'Mishpachas Yehudah" is an added Perush of Beis Lechem. 2 The man was a Levi. You cannot say that he was a Levi from his mother's side! Refer to 17:7:1:1*.
Malbim: He is attributed to his mother because she inherited land in Yehudah, and he lived there. His paternal lineage was from Levi; they did not receive land.
Radak: This is difficult. Where do we find that lineage is attributed to the mother's family?! Do not answer "Eleh Bnei Machir Avi Gil'ad", and Seguv and Ya'ir were from Machir's daughter (Divrei ha'Yamim 1:2:21-23). The verse discusses Ya'ir's cities in Gil'ad (it does not attribute their lineage to Gil'ad).
Radak: The Nun is Menasheh is suspended (above the other letters), to teach that [it does not belong;] he was Moshe's grandson. Due to Moshe's honor, he is attributed to Menasheh, for his actions were like Menasheh's.
Why did he live in Yehudah?
Rashi: His father was from Yehudah.
Radak: Even though the Leviyim received cities, he lived in Yehudah for livelihood. When he ceased to earn money there, he sought another place for livelihood.
