estimated pose to openGL rotation

I have a routine I’m using for pose estimation that seems to work pretty well simply outputting numbers but I’m having a hard time figuring out how to use those to rotate my OpenGL modelmat and do some simple AR overlaying. The rotation matrix returned looks something like this:

0.59 -0.23 0.77   
-0.25 -0.96 -0.10   
0.76 -0.13 -0.63   

Y rotation is pretty reliably 0,0, Z rotation is pretty reliably 1,2, and X is pretty reliably both 2,1 and 2,2

Does this ring a bell for anyone? The routine I’m using is this one: which again, works well, but doesn’t quite make sense to me. I tried to read the underlying paper but it didn’t make a ton of sense to me. Thanks for any advice or pointers,