I think DP Davis's definition of incidence is quite historical and doesn't reflect the accepted modern UK definitions
I think it's a proof reading error, or an error introduced by some one other than Mr. Davies, perhaps an editor even.
The angle of incidence is a term used in the rigging of an aircraft, some term it the mounting angle, the angle twix wing chord and the aircrafts longitudinal axis, the B-26 had to have its angle of incidence increased to improve its take off performance, then again the F-8 increases the incidence by 7° for landing and take off. Even the rigging directions for the 1930's Tiger Moth call it the angle of incidence.
What ever the cause, Davies book is in error.
Then again we can go back to WWI and the Sopwith Camel, incidence 2° both upper and lower wings.
Having said all that I now find myself with a black eye. Just read a 1942 Air Force manual which carries the statement,
Angle Of Incidence - The angle between the chord of the aerofoil and the direction of airflow past it. The angle of incidence is often referred to colloquially as "the angle of attack" and should not be confused with "rigging incidence"
Personally never heard of "incidence" being used synonymously with angle of attack previously.