Ambient air temps play a critical role in thermal regulation. The lung runs down past the heart, liver and the major arteries and veins. When the air in the lung is too cold or warm the blood temperature changes and then drops the temps of everything else. Warming the ventral muscles can only do so much to re heat or cool the core temps. There is some debate about if there is need of a hot spot at all but very little about the need for ambient temps. It is not the room temp that is important but the air temps in the enclosure but the simplest method of controlling the ambient temps is to regulate the room. It can be done with other means I am doing so but it requires care. I believe you will have a hard time finding any care sheet suggesting that 66-69ºF cool ambient or surface (often the same thing) is acceptable. Most state the lowest safe temp (and not for a long period of time) is 75º and that is very very low.

My guess is that the ambient temp was not 66-69 but was warmer. That is a huge advantage of tanks they hold and distribute heat 1000 times better than tubs.