Please look again at the definition of "musical one-hit wonder" in the large callout of the article. That is key to your issue.
A musical one-hit wonder is "an artist who achieves mainstream success for a single song. ("Mainstream success" is often defined by a peak position in the top 40 of the US Billboard Hot 100). The musician may have had successful songs, however, on country, R&B, or other recognized music charts or in other countries."
Beck's song, "Loser," charted #10 on the US Billboard Hot 100, and his next closest hits were in disqualifying positions: "Where It's At" which charted at #61, "E-Pro" at #65, and "Jack-Ass" at #73."
Again, note that success on the Alternative charts, R&B charts, country charts, and charts in other countries doesn't help an artist with mainstream US popularity. This doesn't diminish Beck's success as an alternative artist. Same concept with Oasis. Given that Beck is still generating music, maybe he'll have another Top 40 mainstream hit (rather than one on the alternative charts) and thus forfeit the one-hit-wonder designation.