Continuity mistake: Between Wade stabbing Ajax to the bridge barrier and him talking to Colossus, the sun changes every shot.
Continuity mistake: When Deadpool comes back to the duplex after cutting off his own hand, he grabs a red towel off a Chevy Citation parked outside. When he enters and flops onto the floor, the towel is yellow.
Answer: Yes that would be how she most likely was able to tell.