Mafia 74. Dance of Life and Death

But if he weren't Mafia, would he lie so much about his role?

If a Town member lies about being Mafia, the Town will want to lynch him. Mafia are more likely to advocate for his lynching than to kill him at night, unless he has a particularly important role.
If a Town member claims to be a member of another Town faction, there will be less desire to lynch him, but a greater chance of being killed by the Mafia.
In general, it's hard to say what's better.