They probably had a mistake and just did it accidentally but we don't know if there's deep intention about those duplicated application.
This must be the concern for managers because most of them can't even check each of their participants.
Sometime it is mistake from bounty hunter but sometime it could be from cheater - who want to use other's account name for the bounty and earn more stakes than he could get. I made mistake one time before and I have to chat with BM via telegram to correct it.