Do cold hands almost always mean hypothyroidism?

Unless you have too low blood pressure or blood circulation problems then

Does having cold hands while indoor or in fair weather almost always means hypothyroidism?

Probably. I can't imagine temperature being 98.6+ with cold hands and feet.

And/or high adrenaline, which may be compensating for low thyroid function? I don't know if it also commonly arises in other situations too, but perhaps some kinds of high stress life situations could have this effect?

And/or low CO2 levels, which can arise in low metabolism situations, but maybe hyperventilation can also arise in other situations too? If this is the cause, then attending to breathing habits may make a difference, and you may be able to tell quite quickly. Is your breathing relaxed, nasal, diaphragmatic? If not, retraining these may be a good first step. If they are already good, then checking Control Pause (Buteyko method) can give an indication of CO2 levels and relative hyperventilation.