Manga reader here (and currently rereading) and SPOILERS FOR ANIME-ONLYS:
~!If I remember correctly, it was revealed in the manga that William Minerva died in March (?) 2031, which would be correct in terms of Vylk eating a human 15 years ago with respect to the current year (i.e. 2046), but on the contrary, it was confirmed in the manga that it was Peter Ratri and co. that got Minerva and his fellow conspirators killed off, so Vylk couldn't have eaten Minerva then.
On the other hand, if it was Yuugo that Vylk ate, it wouldn't be correct in terms of chronological events because in 2046, Yuugo revealed in Shelter B06-32 that he and his Glory Bell comrades escaped Glory Bell around 13 years ago. This would mean that Yuugo and co. were stiil in Glory Bell at the time Vylk ate the man that he mentioned, which proves that Yuugo couldn't be the man that Vylk ate.
The pen cap thing that was given by Vylk (that was given to Vylk by the man he ate), though, had the same exact appearance as the one Emma and Lucas found in the floating island thing with the elevator to the human world in Goldy Pond, and had the same vast information (i.e. floor plans of farms, circuitry, etc.), so the man Vylk ate COULD be just a Grand Valley grown-up that successfully destroyed Goldy Pond, but at this point I don't know anymore.!~
