Series/Parallel resonant circuit problem.

I have operated many times an AM crystal radio with the antenna/ground connection direct to the tank circuit (i.e. without an antenna-stage RF transformer and no connection to the center tap of the coil) and it works fine. But I've been led to believe that this configuration is a parallel-LC circuit and basically a wave trap; indeed, I've seen schematics with the same circuit used as a wave trap when used with the primary winding of an antenna-stage RF transformer. I know that it acts as a series-LC circuit when used in the secondary winding of an RF transformer but in this instance it's not used in that fashion. How and why is it working?

Many thanks! CJD