Vince is referring to how Maggie and Glenn seem completely unconcerned about Beth.
In all fairness to Glenn and Maggie, how long has it been since they've seen Beth and what have they gone thru since they last saw her?
After almost getting my head smashed in by a bat then eaten by some cannibals, I don't think I'd even recognize Beth if she showed up in the middle of the road........
I mean, it wasn't like yesterday she disappeared........