When I read Fogel's article I also thought about Bruno Walter. I am not a scholar of historical performances, but I do own the piano rolls recording of Mahler playing and thought them fascinating. From the (admittedly) few recordings that I've heard of Walter conducting Mahler's compositions, I would not have connected him, Mahler's friend (and progete?), to the fellow who sat at the recording piano in 1905. However, based on that sample of the Mengelberg's M4 at Pristine Audio's site, I could connect him to the Mahler on the Welte-Mignon piano rolls. I suspect that the recordings are at best indicative but probably not conclusive.
To Barry's point "that Mengelberg didn't conduct Mahler 4 that way in the previous decades" is easy to accept based on my examination of M6 and M9 timings by modern conductors who have mutiple CDs in the catalog.