My boss discusses my work ethic is this slander?

my boss asked the girl i trained if i worked as slow as i walk, (he's always on my case about walking faster than i do) and she apparently told him she works faster than i do and that she had to pick up my slack, even though this is referring to the day i trained her. And as a result of that he has told at least one other employee that work slow and not motivated. is that slander?