yes and no: they could have one or two, and maybe those one or two lay eggs; the eggs don't hatch right away, then a week goes by and you have a full-blown infestation. (everything you've ever wanted to know about snake mites [PDF warning]).
there's plenty of examples on here where people bring home a new animal, a week later they find mites and they seem baffled as to where they came from lol. it happens, but it's not the end of the world.