Seeds drop from bare dirt near farmland

While working on a plot of dirt, one block of which was farmland with a potato planted, I had Seeds drop into water along with a dirt block, even though there'd never been any grass nearby and I hadn't been carrying any Seeds (since being surrounded by snow biomes meant I'd never had any). Since I'm not sure exactly how to reproduce this bug, I'm attaching a .zip of the full world where this happened.

Possibly relevant: The potato had uprooted several times in the few minutes prior, presumably due to low light since it was always irrigated.