The fact that he insisted on a 6 deck shoe seems to suggest that he was, in fact, counting cards. I was under the impression that standard casino blackjack shoes were 8 decks (machine shuffled).

He may not have played as a standard card counter would (as that would make him more detectable), but he still could have made riskier plays when the shoe was "hot" to give him a slight edge over 49.75-50.25