Definition of "continent" aside, the definition of "continental USA" is yet another different thing. It would seem obvious to mean everything on the main continent, but potentially through some historical quirk it could have meant something else. The only real evidence is how people use it in practice.
The below confusion is likely what happened:
> Some sources incorrectly mix up the continental United States with the contiguous United States (which consists simply of the lower 48 states and the District of Columbia). The contiguous United States (also known as the United States Mainland) does not include Alaska, Hawaii, or any other territories under the control of the United States.