I can't believe it!!! Somebody actually did their own legwork and figured something out without posting pics on the board and ask someone (anyone) else to do it???... but I see from your sig that you might be a Redneck, so that explains it.
Great pics and thanks for posting and figuring out what they were!!!
That is quite possibly the worst thing he could do! Minnow populations in a small pond can take over and choke everything else out. They can become so overpopulated they will rob the pound of all the oxygen in the hottest summer months, and will contribute to winter kill the same way.
By the looks of it, that pond is fine! There will be plenty of perch fry (among others) for the predators to feed on.