I'm not sure what rootstock gets used on crab, probably similar as in other apples.
Your previous tree looks like a seedling,.. there has to be allot of them come up from bird droppings, you can use them to graft any apples on you want, my apples in the orchard are most on crab seedlings.

Windfall:

Ornamental crabaples grown at nurseries usually are bud/graft onto MM111 rootstock. At least in my nursery experience for zone 5 areas.

For very cold areas, crabs are also propagated onto seed grown hardy crabapple rootstocks (seeds from dolgo, Red Splendor or any other zone 4 crab).

And finally, some are grafted to M. baccata, M. ranetka, M.
prunifolia or 'Antonovka' rootstock.

thanks guys,

I don't believe this to be MM111. As I believe that has normal colored foliage.
Given it's location I am sure it was not a feral seedling but a purchased tree. Which makes it seem likely that is was some type of seed grown crab for the rootstock.

A quick search of the other cultivars mentioned (baccata, ranetka, ect...) again seems to show trees with more "normal" coloration of green. These leaves are slightly more heart shaped/pointed than most apple, very dark green base color with a noticeable red/maroon cast. I have seen this leaf type on other red and pink flowering crabs.

It doesn't really matter of course. They are there and I will use them...just got me wondering.