If it is true that this virus is a weapon, I find it very plausible that it was intentionally introduced into the general population. We have seen many examples of questionable behavior over the last few years and it seems it is almost a competition do do the next bigger and dumber thing.
I agree it could be introduced to “check it out”, but if you had a poison that could be introduced into water, would you test it by polluting your own water supply?
Would make more sense to have al ittle bit of geographical separation to do it.