Haha if HR told you you will be working at back office, it shouldn't be a trap as they cannot lie. Still it is just an interviewing stage, why not just go for it and understand more about what would you do with this position if you really take the offer. Ask the hiring manager or even the team head directly!!

As I heard, the salary is not far (seems similar...) to the offer of GGT lol

So yea, try try first.