"terminal masters" more usually refers to a field where a Masters degree is the highest attainable degree, like a Masters of Fine Art (there is no Doctorate of Fine Art).

Although searching Google - I can find references to the usage you're giving.

But, I fully agree that a Masters in a hard science, especially from a top research school, is almost always a consolation prize for those who drop out. My program would not accept students into the program for a Masters, it was PhD only, unless you dropped out.