Looks like a plum to me as well ... strange it has flowered before leaf buds broke....

wow that is a very young/small looking tree to be flowering. They almost look like apricot flowers.I have some plum seedlings I planted in 2008 that are 14 feet tall and are now pushing flowers for their first time this year. Your flowers look very large, hopefully they set fruit and give you some samples! If they are any good I want some scion wood!

More surprising is that it seems hardy there?

You bet..last night we had some frost, not sure if any will take, and still young. I looked closer today and some of the bottom branches looked like Siberian pear, very light in color, no wonder why it was camouflaged amongst the pear seedlings.
I was thinking the same as you Glenn about apricot flowers.
Grafted some wood onto Nanking in the hopes to push fruit earlier, here the branch from below. Thank you all!

Grafting on Nanking causes early flowering? Or do you mean just grafting in general?

Nanking is dwarfing plum stock, [and older] which should come into production earlier...could have top grafted onto plums but have Nankings just a few feet away.