If indeed the flaps were selected at 1, there should have been a configuration warning. Flap 1 is not a takeoff flap setting in the 757.
Only if 5, 15, or 20 were selected and takeoff calculated with another setting, then there would be no warning, but as far as I know, Flap 1 is not on the 757.
If I recall, Flap 1 was only available for Takeoff on the 767-200.
Correct me if I´m wrong...
SEQU