Modulation is a temporary key change. What you describe is a chord change - albeit non-diatonic. It's rather like asking what's the modulation from C to Am. It isn't a modulation. And certainly not a key change, although it can sound like either.
However, my 'bible' labels it as extraneous modulation - if the key has actually changed. I was considering what John wrote, where one minor chord went straight to another, as described, as in 'Light my Fire'.