DNA matches again

[Phoenix]

ES is a close match over 20 cM with me and my cousin (so Mum's side) No match with my aunt (Dad's side)

GS is a 10 cM match with me and also shows a match with ES.

So far so good.

GS is not a match with cousin.

Okay.

But GS IS a match with my aunt.

Does this mean that GS is related to both sides of my family?
Or does the shared DNA match come from DNA which is nothing to do with me at all?