Young Eagle figuring out fetching a ball vs. fetching prey

I was watching young eagles hunt for a few hours by the dog park today, and one of them landed in the tree next to me WITH A BALL in its claw! It flew off with it, came back a few minutes later and dropped it. Guy shows up out of nowhere and asks in disbelief, “did that eagle just drop my ball?!” He’d been fetching with his dog and the eagle swooped the ball out of the lake! A couple minutes later, young eagle returns with a chuck-it ball! I guess they’re figuring out what’s prey and what isn’t!