Could be. How long does it usually takes to build up a population of parasites in a pond that has been dry and cleaned out.
I've seen snails populate an aquarium in a few months. I don't really know how long it would take in a pond, but a year wouldn't be out of line. Now if the snail(s) that somehow got transferred to the pond were already infected, then it might not take that long.
" A swimmer’s itch problem may develop with a few as 2 percent of the snails infected. However, snail populations may be as high as 400 per square meter. One infected snail may release up to 4,000 cercariae per day. At the 2 percent infection rate, this would mean up to 32,000 cercariae would be produced per square meter per day. On a typical 100’ x 100’ beach area, this translates into a potential 30 million cercariae released each day.
Most cercariae are released between noon and 2 p.m. With little free-swimming abilities, the cercariae will swim to the surface to optimize their chance of contacting a suitable animal host. Concentrated near the surface, wind and currents may carry the cercariae up to four miles from the release area.
The cercariae may not penetrate the skin until after the bather leaves the water, at which time the person may feel a slight tingling sensation. The cercariae are soon killed by the body’s natural defense mechanism, but will continue to cause irritation. Studies have shown that 30 to 40 percent of people contacting the parasites are sensitive and experience irritation. Small children playing in shallow water are most susceptible because of the alternate wetting and drying with the arms, legs and waist area most prone to infection."
https://dnr.wi.gov/lakes/swimmersitch/