Guyton is a bigger defensive end, coming in at 285 pounds at 6'2 1/2". According to the folks at ESPN Insider, he was actually the 92nd-rated player in the entire 2012 NFL Draft, and a 71 on a scale of 1-100, so based on that getting him in the seventh round is pretty impressive.
Here is a blurb from that ESPN Insider scouting report on Guyton:
One of two defensive players to win Cort Majors Captains Award in 2011.Winner of Cal's Brick Muller Award as the top lineman on defense and Joe Roth Award given to the player best exemplifying courage, attitude and sportsmanship in 2011. Recipient of Cal's Bob Tessier Award as the most improved defensive lineman in 2010.
Guyton was a second-team All Pac-12 defensive end, and led the Golden Bears in sacks with 5.5 this past season. He also had 12 tackles for loss.
Sounds like a pretty nice steal at this point in the draft to me.