[001hans]

Depending on agreements what 2NT (vulnerable) promises, 5C seems like a good bid: south may assume that it has a good chance of making.
He missed a good chance though telling N that he was assuming that: he should have bid 4S: defensive values in spades in case opps compete on the 5-level. Now N knows that 5H does not stand a chance + that 6C/D is a phantom save: even if only 1 off, then against 5H also 1 or more off.
So, the best N/S auction is 1S - 2NT - 4H - 4S
5H - D (S has either clubs or diamonds, but OW have no source of running tricks apart from trumps)
In case west passes, N bids 5C, and sees S passing or bidding 5D.
In the given auction 6C by N is nonsens: if 5H is making, he can expect 6C to go 2 down.

[dake50]

while I appreciate bidding discipline as much as you, laying unconditional confidence on it might be taking a good idea too far. As you know from practice, some people preempt twice and, what's more, get away with it. Even Robson/Segal admit that preempting twice may be right on occasion.
..As for the hand in question, I admit I would have doubts on whether to pass or bid 6♣. I'll probably end up passing, but I certainly won't hang partner for bidding on -- whereagles

*** Starting out with a bid that lets partner captain, then "no, I won't" is the un-discipline.
Start 2D, then 5C if you think 2 bids are justified.

[whereagles]

dake: two-suited overcalls make partner captain with respect to suit, but not necessarily w.r.t. level.

The point is these overcalls are usually done on a variety of HCP ranges (high-low for some, any range for others [e.g. marshall miles]). So overcaller may well still have a thing or two to say after his partner selects suit.