did I cum ?

During foreplay my bf sucked my boobs. This gets me soo aroused. Right after  I proceeded to go on top to ride him however there was a slightly thick white slightly liquid substance on his penis. He asked what it was so I immediately told him I came. 
The truth is though that I don't know if I came because I never came or had an orgasm before. I just know that cum is a white substance and I know I got very aroused. 
So was it cum or is something wrong with me ?