To temper chocolate, you melt it (getting it up to 120F), cool it rapidly by adding more chocolate to 82F, then warm it to 91F, and then cool til it is pipable. Main point of this commentary is that chocolate is still liquid at 82F after adding the extra, so it wouldnt have to be that hot in the tent to get it to melt. (though it technically melts around 86-90F on its own). He should have realized how hot it was and used caramel. Or meringue (with the blowtorch to make it brown). IMHO, this was a bit of a failure on Steven's part to adjust to the conditions. He had options, just didnt use them.
Many shows like this have VERY limited A/C - the main other example I will showcase is Bachelor in paradise - there is no A/C on in the resort, because A/C messes with the audio. So I think that the tent has generally been a good option because England is usually so temperate. But it was really hot the last 2 summers in the UK, and in June 2017, it was hotter at Heathrow than it had been in 40 years (34.5C ~ 94F) . (The filming locale is just west of Heathrow, so that's pretty representative of the temp). I don't know exactly when the show films, but based on the comments about exams and such, id say it starts in the spring and ends in early summer so it can air in August. That would put the last couple weeks right around that late June heatwave in 2017. Average June High Temp is 20C ~ 70F, so you can see why the bakers struggled. This is soooo outside their norm!