That's a bit of a stretch, isn't it?
Thomson's usually a little more nuanced, I'm sure she qualified things better than that.
The problem already is that J/P is based on which function you extrovert, NOT on your dominant function... and introverts extrovert their secondary while extroverts show their primary. So I'm not sure that statement even makes logical sense, even before dragging actual biological facts into it.
I think this is related to the way Adymus talks about type - dividing all the functions into two categories: Adaptive and Directive.
Adaptive:
Ti
Fi
Ne
Se
Directive:
Te
Fe
Ni
Si
Basically P types are those who have Adaptive functions as their top 2 functions (eg an INTP, with TiNe) and J types are those with Directive functions as their top 2 (eg an ENFJ, with FeNi). You can test this if you want, by going through all the types.
Adymus' method of visual typing (watching the face and inferring which portions of the brain are being used) ties into this very well: Ni and Si are indicated by eye-drifts to the left (J/Directive/left-brain), whereas Ti and Fi are indicated by eye-drifts to the right (P/Adaptive/right-brain).
The other functions are indicated by cues that generally don't conflict with the right-brain/left-brain hypothesis.
Anyway, I've found his stuff is mostly in line with Thomson's, and XXXX seems in line with him, so perhaps XXXX isn't totally off.
IIRC, Thomson called Ti and Fi irrational functions, which I found odd - along with Ne and Se, yet Ni, Si, Te, Fe were rational functions. Again, this matches the Adaptive/Directive divide and visual typing cues.