The C++ standard doesn't describe registers. The compiler can put whatever it wants in them, but it must do so transparently.
I just want to use the correct term when I talk to my colleagues
The right term is in the header of your quote, "automatic variables". Or perhaps "local variables".
"Stack variables" would also be often understood to include all automatic variables, both in registers and in the actual stack. But this term is prone to "C++ has no stack" nitpicks, as the standard doesn't call it the stack either.
I clarified by specifying Windows with MSVC.
Honestly, I don't see what this changes regarding the choice of terms. If you don't discuss specific generated code/assembly, you normally use abstract terms defined in the standard, so you don't concern yourself with registers.