There is a chance that she lied, but like 1%. Then there is 99% chance that her boyfriend does = have a stutter and it's just less severe than yours. I don't stutter much in low stakes situations, but I can't talk at all in front of the audience and get massive blocks and ticks. I used to stutter more when I am depressed, under a lot of pressure, etc. Just because someone appears to have better speech than you does not mean their stutter does not affect their life, maybe it was very hard for him to talk to you fluently or it took years of work to get there. Anyway, you should just talk to her about it. Don't speak from a place of anger or accusation, but rather from a place of curiosity, stutter is very unique for everyone, so if you want to know what his deal is just ask. Say something like - I did not hear your boyfriend stutter at all when I spoke to him! Does he only stutter when he talks to a bigger audience? Good luck!