What I mean is people will use emulators to create another account to get a desired hero and they will trade that desired hero to their Android game.
For example: Suppose I play Fire Emblem Heroes on my Android and I want a 5 stars Ryoma with perfect IVs. For that I will use an emulator to reroll until I get a 5 stars Ryoma with perfect IVs. When I finally managed to get one 5 stars Ryoma with perfect IVs, I will trade that 5 stars Ryoma (From the emulator) in exchange for my 3 stars Virion (from my Android) and that's it. Now I have a 5* Ryoma on my Android.
The same goes for getting a +10 of these heroes: Brave Lyn, Brave Ike, Brave Roy, Brave Lucina, Brave Veronica, Brave Ephraim, Brave Hector and Brave Celica, because these heroes can be obtainable once for free per game, so if I'm using an emulator, I can get multiple copies of these heroes and send them to my Android game.