Horizontally it's 6 squares away..
Vertically T is 2 squares away, whereas 5 is 5 squares away, which I think is causing the confusion.
But I agree with you that 5 isn't valid.

Just play GG t/A and that solves the problem

Nobody is correct. () There's not really a vertical/horizontal to be considered. Both are 6 squares away, which is the only uom in the game.

Yes exactly.
Both ate 6 squares away when played by the rules.
The problem is people are looking at the vertical distance and the horizontal distance wrong as opposed to just..

X squares in whatever direction whether that follows a diagonal or straight line.

Just to play devil's advocate:

Mathematically (according to trigonometrical theory) 6 spaces diagonal is actually farther than 6 spaces vertical or horizontally. It will be 1.41427 times as much. So 5 space diagonally is actually more than 7 spaces straight.

I'll stop before someone hits me

While your mathematical statement is true, it's not how the game works..
But this game has always left the ability to surprise people by just how far you could move on the diagonal.