You might hear someone mention washout, mechanical twist and aerodynamic twist, and it might happen all in the same paragraph. You pegged the fact that those people mean washout when they talk about mechanical twist. The aerodynamic twist they might mention is not a twist at all, but differing airfoils from root to tip. It is just the use of a different airfoil at the tip that stalls later than the airfoil of the wing toward the root. Needless to say, that wing will have a progression of airfoils along it's span.

Keep in mind that the Reynolds number situation that's being talked about is based on the different RN a tip with shorter chord will have versus the RN of the rest of the wing. That creates a disadvantage for tips and helps cause the "tapered wings stall from the tips" result.