Shogun is very capable on the ground, and unless he and his brother Ninja are telling wild stories, they began training in BJJ first as children. They literally grew up grappling.
Obviously Shogun was famous for his devastating MT, but knocking guys out in the first round for the first half of your career doesn't mean you are not a ground player. Take Jose Aldo for example.
Suffice to say that out of his 10 career losses, Shogun was tapped 3 times. Sobral - who is a world famous competition level early jiu-jitsu player at the time, Forrest and Sonnen. Chael is an excellent MMA adapted grappler, go rewatch him putting away Brian Stann with an arm triangle, look at his setup and adjustments.
I would be willing to bet Shogun had 5,000 hours on the mat before he fought Forrest the first time.