I see liquid in the roasting pan yet the cauliflower is well drained before roasting. Does this liquid exude from the cauliflower as it roasts?

Roast it on a mesh rack over a sheet pan.

Yes, cauliflower can exude a great deal of liquid as it roasts. One that has been simmered in liquid would certainly do so, even if it was well drained. The cauliflower itself is a high water content veggie, and it would not be able to release much in a pot filled with water. So it would do in the dry heat of the oven. To help combat the accumulation, you'd want to use a very large skillet or low rimmed baking pan, much larger than your head of cauliflower so the liquid would stand a chance of evaporating at least as fast as it was released. However, you can drain it off periodically if needed. That would help with browning on the bottom, rather than having it finish stewing in the juices.