It would be trivially easy for a hostile power to covertly release a pathogen in another country.
It would also be trivially easy to engineer simultaneous release in multiple locations.
It would be less easy but not impossible to take an existing pathogen during a pandemic, engineer a variant, and release it in another country.
There would always be ambiguity and uncertainty about the source, because there are no telltale markers that unambiguously define an origin, or even whether a pathogen is natural or man-made.
I am not suggesting any of this happened. But I am pointing out that biowarfare has some unexpected covert possibilities.
While Covid may or may not be an example - insufficient data - any defensive strategy should consider the possibility that some other pathogen might be seeded deliberately.