I saw the statement below in this answer:
Note that for normal level unaccelerated flight $C_L$ is always > 0. The minimum $C_L$ is a negative value for negative AoA, and would mean that the aeroplane is flying upside down.
This would seem to me to imply that flying an airplane upside down implies a negative angle of attack.
But the typical illustration and explanation of angle of attack is that it is the angle between the airstream and a reference line, the latter of which in airplanes is normally the wing chord.
How can the two be reconciled? Alternatively, what am I missing?