Yes, various terrestrial sources have been proposed for this signal over the years, primarily because of its strength.

To have an extraterrestrial origin, and still be so anomalously strong at the point of reception, it must have been so strong at the source that it didn’t fit any known cosmic process. Given the inverse square law, the easiest explanation for the unusual strength was simply that it was unusually close. But this work seems to rule that out and also propose a process to create such a strong signal.