Why did she taste something when she did this to me?

My girlfriend gave me a bj the other day. I didn't c*m yet she said she tasted something. She said it was salty and I'm wondering how she got a taste from it when I didn't even c*m. There wasn't even prec*m, not even before she started. She told me maybe it's because I used the bathroom a bit before hand but I'm not sure if that's really why.