His remarks are open to interpretation. Note however that he said that "They're not sending their best". One could interpret that to mean that he believes Mexicans as a whole are a fine group of people, but that those who immigrate from Mexico to the US represent a "worse" subgroup of the total group. Charitably, I think this could be characterized as meaning somewhere from "many Mexican immigrants are rapists" to "a higher-than-normal proportion of Mexican immigrants are rapists". In fact we know that immigrants commit crimes at a lower rate than the non-immigrant population.

And setting aside the close-reading and the statistics, we should not be naive about his intention, which is to characterize Mexican immigrants as dangerous criminals. Again, should I have to wonder if my coworker believes this about me or my family?