If he had a metal lathe yes. Clearly he's not a metalworker. But it was still possible he had a wood lathe.

I guess you could cut stainless steel tube on a wood lathe, slowly, maybe? But you'd have to make that plug to hold it on the lathe anyway, at which point it's faster to take it out and use it as your clamping jig on the cutoff saw. Not to mention safer