Flight path angle should not be confused with pitch angle. Pitch angle is the angle between a line drawn through the aircrafts nose and the horizontal. Flight path angle is the angle between the the aircrafts velocity vector and the horizontal.

Descending at a constant mach increases the IAS which means the descent angle will increase but we will be reducing angle of attack to keep the lift formula in balance, so pitch angle will decrease.

Now terminology and interpretation become a factor in answering the question. You could describe a bigger nose down pitch as either increasing the (negative) pitch angle or decreasing the (positive) pitch angle. The examiners’ view is that, if you move from a cruise pitch of 2-3º up to a descent pitch of 2-3º down, you have decreased your pitch angle.