A "very high number" of Lesser Yellowlegs indeed, but not unprecedented. On July 27 last year, Dave Shepherd called me to say that he and Julie were watching a BIG flock of Lesser Yellowlegs around Tern Island (Daniel's Point, Trepassey). I went over and was able to count about 85 Lessers plus a handful of Greaters. Later that afternoon I came across what I assumed was the same flock on a gravel bar at the SW end of Biscay Bay Pond, and tallied at least 77 Lessers.
I find it intriguing that while Greater is Newfoundland's common, "default" Yellowlegs, Lessers are roughly 10 times more common than Greaters as vagrants to Britain.