Roger fight Linlin when she was in Rocks, same as Garp...BM remember Garp, so it is not clear how many times she loses, or even not clear that she lose at all. I mean, why she is still alive and clean?! Also Roger decided that it is better to sneak in and run then face her...or maybe he could have sex with her and run away when she sleep...
Actually for me that could be the case, and well thing that Pirate Roger could done with her...so that is something that could be called as trick or robb, case you know imagine how Roger comes to Linlin(in her youth she was hot as) and said something about them making alliance, then they drunk and to things between he-he, while when Linlin was asleep,(which reminds Brook), Roger woke up, got copy from poneglyph and run away. That could explane why BigMom call that unfair, and that Roger steal copy from her.