It lives in the water pipes. There's a good chance it's already in your frog's water dish (and in your drinking water). The only reason you see it on the humidifier is that the colonies have been undisturbed long enough to grow to a visible size. I've not seen any studies about that specific bacteria and amphibians, but I imagine it's harmless since it's so common. If it wasn't you'd have seen something about it.
You're talking about the pink stuff like what you see making rings in bathtubs, right?
Since you used vinegar in the humidifier, maybe run it in another room for a day just to make sure all the vinegar is gone. For the tank and water dish, normal cleaning should prevent excessive buildups of any bacteria.