Being developed could point to two sources: lab mutation and naturally occurring mutations.

emerging, does not negate a lab source, but seems more natural instead of artificial.

Since he is a politician, he has to weigh his words to convey the right impression based on people's tendency to stick with only one immediate and simplistic meaning.

However, both would be ok, and an eventual follow up question has the potential to pinpoint meaning exactly.

However, then he would have to lie.