Red Maple with Sugar Maple Leaves?

[Andy VT]

My suburban neighborhood is loaded with all sorts of maples including many red maples. Every red maple I've identified has what I think of as the quintessential 3-lobed toothy red maple leaf. But one tree that had red buds this spring at the same time as the other red maples and seems to have red maple bark has leaves -- all the leaves -- that are quintessential sugar maple shape... full Canadian flag leaves. The owner of the tree swears it is sugar maple based on the leaf shape. But I can't get past the red buds, timing of the buds, and the bark.

Anyone got an explanation for this tree? Do reds and sugars mix? I am assuming the tree, now very mature and in fact dying, originally came from a nursery.

Andy