As far as I know JAL sets cabin temperature to 82F (28C).
It's possible that although while you were told that it was 76F, it was actually at 82F.
Whether or not 82F is hot or not can be debated, but considering that the Japanese government asks people to conserve power and set their air conditioning to 82F or higher during the summer months, the fact that they are asking people to make a sacrifice implies that 82F is hot.