I understand what you are saying, but we need to understand that "wild plum" here doesn't mean "the wild ancestor of the domestic plum", which it is at risk of being misunderstood as. I don't think such a wild ancestor really exists freely growing in the wild and reproducing. I don't think that's what you get if you germinate domestic plumstones.

"Mirabelle", whatever that means, is commonly sold as a hedging plant, so if some trees are not inconsistent with the kind of thing that is sold is Mirabelle, lets call them that, being aware it is a rather vague description.