If the frame was that soft the gun would have come apart on the first shot.
He's shooting a pretty mild load. The cylinder is taking most of the pressure. Original Colt SAAs were made out of cast iron for cryin' out loud. I suspect that for this particular gun/cartridge combination, this frame when in good condition is capable of handling a LOT more power than the 44Spl can dish out, likely by over 200% if everything is good.
Or put another way: in terms of stress on the FRAME, I'd be willing to bet the 357 version of that gun is under more stress with top-end loads than the 44Spl version.
Therefore, a bad heat-treat on a frame that's only running at half strength might still easily digest 500 rounds of mild 44Spl without drama of any sort.
IF this is what's going on, it could turn around and bite him at any time, either from a slightly over-pressure round or if he attempts to shoot anything serious in it, 250gr hardcast out past 1,100ish or so. OR, it'll suffer from slow "stretching" sort of like happened with the earliest S&W stainless guns.
If it's flame-cutting, and yeah that's a big "if", it needs to go back to Ruger to get the cylinder frame Rockwell tested in an unobtrusive place, like say under where the grip frame meets.
Remember, we have reports of what appears to be a "tray load" (however many that is!) of LCRs that seem to have skipped a heat-treat step and yet again are suffering rapid erosion. Two people have reported this issue that I know of and yet the guns still held shooting 38Spl.
It seems quite possible to me that the 44Spl could have had the same thing happen.
On the flipside, it's possible that what the owner of this gun is seeing is a pattern of lead or crud deposits that have a channel in the middle that looks like flame cutting but isn't. Shooting plain lead bullets, this is perfectly plausible. If it hasn't been done already I'd try cleaning the area in question with standard methods compatible with blue guns, do a thorough job and then re-evaluate.