callicladium's Identifications

I have been observing this crabapple that volunteered along a fence line (almost certainly from bird droppings) for a few years now. It is not our native crabapple, and doesn't appear to be M. domestica, though it could be a hybrid of one of those (or completely unrelated). It really doesn't seem to match any species description I can find and is almost certainly a hybrid of some sort.

I have included pictures from bloom time and also fruit both under-ripe, fully ripe and bletted (a natural softening of the fruit that turns it into edible mush).

The tree is very compact and has quite an upright core with most branches emerging at nearly 90 degree angles.

If you have any guesses at what the ancestry of this could be I'll be glad to hear your input.

The flavor of the fruit is very citrusy like kumquats, but without the burn. When fully ripe the flesh of the fruit is yellow just like the skin. When bletted they taste similar to tart medlars with a higher moisture content and seem very resistant to rotting (probably due to the high acid content).