what is: "construction crews" and "flyby castings"

[Norfleet]

A construction crew is a team consisting of one or more commanders, often mages or priests who are responsible for the construction of a fort, lab, and/or temple. Often they're the same units that conquered the province in the first place.

A fly-by casting can include such a behavior as you described, as in the term "drive-by priesting", a hit and run priest attack which is fun to do against AE Ermor. In this case, however, it is a battle that resulted as a result of a flying SC being rudely intercepted at a waypoint en-route to the front line by an attacking army: It was "fly-by", because the unit in question was flying, and because that was not his actual destination. It is definitely rather humiliating and/or inconvenient to have your army accidentally wiped out by piecemeal forces en-route to the actual front line because said forces happened to be in the wrong place at the right time. Or maybe it was your army that was in the right place at the wrong time.