5 eV converts to around 58,000 K (the tests were done with copper cathodes)
It would have been interesting to monitor monochromatic lines corresponding to heavier fusion products. Production of helium and heavier elements apparently is common despite the fact little to no effort is generally spent on identifying root-cause.
Between some of the first publications I've read (sorry I discarded them all, but I remember starting from Egely's long video, timestamp 15:25 "The Production o f Neon and Helium by the Electrical Discharge" By J. Norman Collie, F.E.S., Hubert S. Patterson, and Irvine Masson then going through references looking up subsequent follow-up work) was a series of investigations on alleged adsorbed and absorbed neon by electrode metal at foundry/production stage/whatever early stage, and no amount of vacuuming with heating, boiling, evaporating the metal managed to release the gas, only ark discharge. Go figure. I recall authors concluding to unknown effects for those poor neon atoms hanging on to the metal . I imagine love was the force, or something divine, and only zapping them with high voltage managed to break the bond. The so obvious - obvious at a level where it is already invisible - "duck" effect of possibly PRODUCING neon was I guess excluded on the basis it's not even remotely possible. It is forbidden to think about. It's like the statement on Jaitner's webpage "Physicist Neils Bohr insisted that Langmuir's results could not be correct since they violated conservation of energy and persuaded Langmuir that publishing them would ruin his career".