The assumption that the antenna is just a straight wire is wrong. That was demonstrated by Mr. Glenn with his rotating dipole experiment.
What is not mentioned is that almost all of the trucker CB antenna arrangements are short monopoles. In order to make the antenna shorter there is a coil (balun) incorporated. usually about 1/2 way up the whip. So now you have everything needed to generate the spark. A Coil moving through a very strong E-field and a spark gap.
The antenna did not generate a spark when stopped because it was then acting as an E-field sensing device. Not enough voltage to spark. Now move the coil incorporated in the antenna's balun and we have all the parts of a generator based on a fixed E-field. (Most generators work on a fixed B-field.) One or the other must be moving to work.
Kudos on the metal ball on the antenna for static reduction. E-fields form "normal to" or directly out from a metal plate. make a sharp point the the field will concentrate to make the per-unit-area charge equal over the entire object. Lightning rods usually work by "bleeding off" charge through this corona effect without "drawing a spark" less charge in the locality less likely a lightning strike. and if one does occur there is a path to ground that will unusually cause less damage going around the building than through it!