The use of "voices" to denote cultural/ethnic background is common and apparently accepted (at least in North-America). Some examples include stuff like "camarade, da, ..." for Russian, "eh" for Canadian, cowboy lingo for Texans, etc... It's prevalent on TV, specially in sitcoms and animated shows.
If you find that offensive, fine. If you feel the need to point it, fine. But don't call people racist or accuse them of using racist slurs when they probably didn't intended like that.