He got hard when we hugged? It was really awkward :/!!!!?

I went to my close friends house this afternoon and he asked me for a hug and he squeezed me really tight :S I felt him go hard and It made me feel kinda uncomfortable cause hes a friend, I didn't do anything but he just kept me pressed against him, when I left I was still abit baffled lol. what do I say to him? shall I just forget it ever happened and act normal ? the reason it was so awkward is cause were like bessst friends =/