Mostly plants...so I guess they hitched a ride.
My daughter had a plant she'd saved from my Dad's funeral. It got white flies. We tried everything chemically to get rid of them. Like bug bomb set off in a small enclosed space, remving and tossing soil, and washing with rubbing alcohol, dawn, listerine every surface of the plant we could, plastic bag for three days and spraying house and garden aerosol into the bag, then reclosing it tightly. The damn things still lived. She finally tossed the plant. Guess we should've tried sticky traps.
Hitching a ride is a likely scenario to be sure.