Summerizing (Starting) A Previously Set-Up Pond

[vertigo72]

but still, the 2900gallons at 5ft (1.5m) is a lot (~11000L/hr).

You're right, I missed that the 2900 gallon spec was at 5ft head, which is probably not far from what it has to do in that pond.
Its hard to guestimate flowrates from a picture, but I agree one would expect to see (a lot) more water.