--blind response--
There's a
thread over in small stakes about the common trend of checkraising multitabling tags when they've shown they can lay down a hand.
I don't know if this guys is pulling a move on you or not, but I don't think he's sophisticated to be trying to read your hand. Even passive players can do nutting things sometimes.
In the heat of battle, I tend to threebet the checkraise and fold the turn UI if he caps. 50 vpip guys are scattershooters that don't bluff too often. They like connecting and valuebetting instead.