My hunch is he didn't know about Samuel. The arrest affidavit says the officer had to ask TB where the boy was and when he pried open the lid of the tote, he recognized the smell. The officer didn't state the smell was noticable when entering the motel room. Perhaps the bag, duct tape, and tote concealed the smell.
I think the pick-up truck driver really thought he was helping TB get out of town after an "altercation." I'm guessing later that day he found out what TB was doing and then called LE.
I don't think he knew anything while he was actually with her.
Whether he knew or not, the facts are that he checked in motel room with TB at 3;30am, brought in the tote at 6am and then left.
jmo