Many of the plots have recently been “seeded” with mung beans.
Maybe a disgruntled sprouter who couldn’t wait (they look like they’ve been soaked for sprouting)? The beans are sprouting now and if you want to keep them they may grow to maturity, depending on the variety, but they don’t like the heavy soils of Oakvale Green so don’t expect much. They can be turned into the soil as added organic matter so no worries.
Update (Sept. 3): here are a few plants that i transplanted to a planter box at home: