Maybe the odd drop in temp is bearable, but prolonged cold does the main damage?
I think that is very likely ... it will take time for cold air to reach into the leaf / impact its chemical processes. On a cold night at this time of year temperature falls steadily from, say, midnight until dawn and then as the sun comes up it rises sharply, particularly in a greenhouse where the indoor temperature lags behind the outdoor, so the length of time the plant is "cold" is relatively short. That is in contrast with earlier in the year where the temperature falls (to several degrees below zero) and then stays there for several hours during the night!
I do this every year and experience similar temperature variations without any perceivable damage. Perhaps there are other factors which contribute.....
My view is that without a controlled experiment, side-by-side, it is not possible to determine what the actual damage (if any) is. People do it, even getting purple leaves, the plants recover and all seems well. People repeat the cold-shock in future years ...
What I don't know is whether this makes any material damage. Less yield, less sweet / less flavour, sufficiently stressed that the plants are weakened against disease - maybe they would survive a brief infection of blight if they had not been cold stressed earlier in the season? ... that type of thing. In many years the plants won't be subjected to blight (well, not here at least!) so difficult to say if they would be more susceptible or not.
So in the absence of any evidence that it might/might not be detrimental I take the view of avoiding cold-stressing my Tomatoes as I absolutely hate putting huge amounts of time and effort into growing to then have failures / poor performance ... I would prefer to use my time more productively! so I avoid cold-stress, I plant late to avoid having to mollycoddle on cold nights (e.g. I plant all-but-a-few Potatoes late to avoiding having to protect the whole crop against frost, and so on)