This is a poll about left-right preference
Technically you are right about the poll. But this doesn’t change anything. The outcome of poll about left or right and top or bottom won’t be 50/50.
how existing tradition can explain the data with no additional assumptions about physiology or different cultures
The tradition doesn’t explain. It doesn’t have any relation with virtual board. https://senseis.xmp.net/?PlayingTheFirstMoveInTheUpperRightCorner
Polite corner is upper right, under the assumption that that makes playing in their lower right convenient for your opponent
On virtual board upper right corner is upper right for the opponent. On real board it is lower left.
I found another thread about first move etiquette First move etiquette - #3 by mark5000
I have a strong belief that human perception doesn’t have symmetry under board rotation.