It is tough to say if it was a cheap shot. It certainly appears to be, but everything is moving so fast mid-play, it is hard to tell whether or not he did it on purpose. Being a Broncos fan who hates the Chiefs, I am inclined to say yes it was a cheap shot.
As far as wearing a cup, that is just something you cannot do if you hope to maintian your quickness. Back in my playing days I started at CB, and never once wore a cup. Never got hit there either, thank goodness. It gives you a decided advantage as far as agility and speed. Most WRs in the NFL don't wear any leg pads and the smallest shoulder pads allowed, it is risky, but just makes sense. You have to get any edge available, save steroids.