Windows 3.0 came out in 1990, whereas the Atari ST came out in 1985, so that story definitely doesn’t check out. Windows 1.0 came out in 1985 (though still much later than the ST) so maybe it was that?
I just wanted to add that the TOS ROM chips in the Atari ST were 192KB in total which is an order of magnitude less than what Windows would require. I'm assuming GP is thinking of another machine (maybe the TT / Falcon?)
Not the OP but I wonder if he's thinking of Windows 1.0? Wikipedia does describe Microsoft approaching Tramiel[1] but the details differ from what the OP suggested.