
I know nothing about boxers but maybe the owner was referring to what the breeder had told about lines the dog cames from; generally being larger and of course having tails as docking has not been allowed for quite a few years...
I would imagine for example a boxer coming from few generations of US bred dogs will have a different look to it compared to for example German bred boxer?
Fashion, what wins in the ring will have an effect on what people will thrive to breed in different countries...