Low PQ planets have a population growth cap. You can ferry more people onto the planet, but the planet won't grow above that level by itself.

This is not new to the game, it's been around for a while.

Yeah, it's a bit of a bugger. Incidentally, unless you're rigorously playing in character I'd take the neutral or evil pick in this event, as it's one of the nastiest ethical choices. If you're a good race such as the Drath or the Altarians you'll normally have the ethics points to absorb a few acts of gratuitous malice in the name of PQ. That said, the Altarians, Drath and Arceans now have projects to offset low/reduced PQ, which is handy...