Hey Tom,
I think what may be throwing you, is the alternating bass when you go to the C chord. The boom chick strumming stuff is in the country courses, and there's more of it in the bluegrass lessons I have.

http://www.guitartricks.com/tutorial.php?input=574
http://www.guitartricks.com/tutorial.php?input=587

The bluegrass rhythm guitar tutorials are faster, but they show pretty much the same thing. They also feature the same thing using different tempos.

If this doesn't help you out, give me some more details, and I'll do what I can to help you.