I cant speak for 10NL, as I've only played 25NL+, but it's completely reasonable to c-r here if you're SB with any hand or bluff as most button raise ranges are pretty wide. My read here is that the x-r is just exploiting the likely continuation bet that button will throw out on that board and a x-r is a decent play against his range. If he's really nitty, then sure he may have caught a good piece of the board, but without knowing his cold call by position stats, I wouldn't be narrowing his range down so quickly to a set of 6s. He may have any A, two pair hands like A6, K6s, or even a K with backdoor draw like KQs.

For example, last night I was playing a 6max session and my button raise % 1st in was sitting at 76%. Most players at my current limit hover around the 35-50% 1st in raise, unless they're complete nits. With that range, if I was sitting in villains shoes I would definitely increase my bluff range against a cbet (although I'm also aware of that so my cbet % personally is reflective of that)

I personally see c-r on the turn as being much more indicative of strength. I'd be much more worried about that set of 6s if he x-c flop and x-r turn.

I don't think I'm ever folding that flop to such a pissy min-raise without really solid reads