AFAIU, the star being lensed was within the Milky Way, so they could establish some limits on the size of the lensing planet. The upper size bound in the paper

AFAIU, the star being lensed was within the Milky Way, so they could establish some limits on the size of the lensing planet. The upper size bound in the paper is 2 earth masses. (Jupiter mass does come up, but only in the context of a binary system - when ruling out that this planet is orbiting a star, they can only rule out a parent body larger than a few Jupiter masses.)