They didn't compare Ossian to Homer. Read it again. They compared Ossian to Irish legends and then compared The Odyssey to The Illiad. Ossian was suspiciously close to the Irish where Odyssey and Iliad were quite different.
We compare the connectivity structures underlying the societies described in the Ossianic narratives with those of ancient Greek and Irish sources. Despite attempts, from the outset, to position Ossian alongside the Homeric epics and to distance it from Irish sources, our results indicate significant network-structural differences between Macpherson’s text and those of Homer.
https://www.worldscientific.com/doi/abs/10.1142/S02195259165...