Most likely is somebody with a male nearby. Pollen from China has been found in traps in California. However I would guess one is very close to your grow.
I was thinking male near by also but I was unsure of how far pollen would travel. Just wonder if it's a good strain that inpregnated my girls. Maybe they will cover the water bill for the babies.... lol jk
In Colorado I had "road weed" pollen hit mine one time. Hemp. Worthless except for oil or rope or fiber or . . . .. Nebraska and Kansas have it all over the place. The damned cops bust these yahoos who think "free weed!". It's worthless but still gets you charges as it tests positive for THC no matter how weak.
Ya in high school I did a summer job on a farm in Nebraska. The old man laughed at me when I tried smoking that crap.
I was an idiot that tried smoking that crap.From Texas driving through Oklahoma and stop to piss by the roadside at night. What's this? Holy shit it's pot! A few days later after impatiently waiting for it to dry I was sure some horse was missing its breakfast. I was a whole lot younger and dumber back then.