What type of "grass" was that?
Looks good. Everything I mow is KR bluestem and it always leaves stubble growth that makes it look like I didn't overlap. Shredder is set up correctly. Best I can guess is this is left when the blades blow it down so it doesn't get cut. I had to run over and re-cut that since the landowner is really picky.
Don't know if you can see it, since photo doesn't really show it.