Please help 15 year old puberty questions?

so like the other day i was in the mall and i was in the restroom and this guy who was a little older than me im 16 came in and was like changing clothes in a stall with door open and he had no pants or boxers on and he was hard...i went to wash my hands and saw all of it he was just casually changing clothes but im soo not gay i date girls but this turned me on soo much i had to go in a stall my self because i squirted everywhere i was really embarrised even though noone saw but is that normal to get turned on by that?? serious answers please