How???

J6
KQT7
AQ72
A93

5
J6532
KT5
KQ86


MP-pairs all green, South deals
2H* (pass) 4H (4S)

2H: Muiderberg: 5 card major, undisclosed 4+ card in a minor, <11
points
4H: to play, can be very variable in strength


4S is only down one, so bidding 5H is the winning action. However, who
beteween North and South is the one that should bid it?

-The singleton spade is essential, but in my view the preemptor does
not mingle further in the auction unless partner asks him to.

-Being North, I would have doubled because of my doubleton spades.

I fed the hand to Jack 4.0 (former world champion computer bridge) and
to my surprise Jack made the North hand bid 5 H!

Who explains it?