I think two things are being confused here:
1) B.dendrobatidis being inadvertently moved around the Americas [that is, "into California"] on the nets, boots, etc of scientists [or hunters, fishermen, hikers, hobbyists]. While there may be some specific instance of this, the earliest evidence I have heard of this fungus in the wild was 60-70 years in Quebec. Additionally, there seem to be strains native and endemic to the Americas [Brazil at least]. It's been spreading in the wild in North America for decades.
2) B.salamandrivorans was imported for research [not specifically to California, and not into the wild. I haven't anything new about that, but have yet to review this paper.
I think, realistically, we should have learned by now that the diseases we should be most concerned about aren't the ones we know about, but those we haven't discovered. The epidemics and disasters are almost always NEW diseases [or newly discovered]. The only effective solution is to ban ALL human transport of living organisms between continents and other isolated land masses. That includes people. Unpopular and unrealistic, but the only one which would be effective.