Couple of things that have made me think. Firstly I started looking after "walking cargo" in the days when smoking was still the done thing, and the number of times on a night flight a pax has fallen asleep with a lit cig, it was only a serious accident waiting to happen. Here in the UK , it is only an offence under the ANO to smoke in a part of the A/C that has been designated non smoking [for the most part that is all of the A/C] however I still do get flights that are designated smoking flights from the UK. and even on those, pax still insist on smoking in the toilets. With regards to the capt who kept the pax on, Ok maybe he was a little OTT, but we dont really know the full circumstances, ie how many times had it happened, did he seek police assitance and it was refused, or simply was he hoping somebody would shop the offender.
I have had smokers onboard many times, some just involve a simple "telling off" others get the "captains letter" treatment, however I have had 1 or 2 persistant offenders who thought they were untouchable, but they were wrong. Not only do they get met by the authorities but if it is on an outbound flight, they get refused return carriage, and the smug grin is soon wiped off.
Smoking on an A/C in secret is dangerous and the offenders should be sought and dealt with, but at what cost really is up to the crew and the cirumstances on the day, as I am sure this capt thought he was making the right decision in his circumstances