If it was a few large files as opposed to many small ones, this is totally believable. iPhones have Wi-Fi 6E chips, and an ad hoc network where the devices are right next to each other can actually reach the theoretical max speed of the protocol (as opposed to real-world connections to a base station, which never do). I've never measured it precisely but I've transferred ~1 GB disk images over AirDrop in a couple seconds.