You have a fairly close DNA match who has a short tree attached to their results. Let’s assume that your tree through the more recent generations is pretty accurate and you match all your “known” close relatives who have tested at DNA levels consistent with the perceived relationships.
And yet this close match makes no sense at all.
It could be that the DNA match’s tree has an unintentional mistake, perhaps a parent that was believed to be a parent was not. Perhaps a grandparent they thought was a grandparent was not. Keep yourself open to this possibility–again this is assuming that your own tree is correct.
Also tread lightly when suggesting that the submitter has an error in their tree–especially when the potentially incorrect parentage is recent. This person could be discovering that the person they thought was their parent or grandparent is not.
Sometimes that’s not an easy discovery to make. Put yourself in their shoes.
And maybe before you contact them with this possibility, take another look at your tree–and make certain it is not where the problem could be.