I had to go there again and look for the situation (yesterday) ... And I even had to split the path ... Because half of it is surface=stepping_stones (in the grass) + material=sandstone (stepping_stones is a new value for me … I only knew it with ford=stepping_stones) and the other half is surface=paving_stones (which then gets paving_stones:material=sandstone and material=sandstone should be removed if I understood it right).

By the way: I checked another place yesterday, a large park with lots of changes by your mechanical edit (bot). And there, in 99% of all cases (> 90 ways), I had to change material=sandstone to paving_stones:material=sandstone  (because it was ALWAYS surface=paving_stones – except one case where steps were a mixture of sandstone plates and granite sett – I decided to set only surface=paved here. Mixed surfaces are also not very nice to tag ...).

And other mappers here in the region have started adding surface tags to paths tagged with material=sandstone, but have NOT changed the material specification from material=sandstone to paving_stones:material=sandstone in the case of surface=paving_stones. This special case is not very pleasant and again gives rise to discussions and inconsistent tagging and perhaps necessary corrections. Not very nice ...

And this case is VERY common (with sandstone, which is very common in my region). 

I checked it with Overpass-Turbo. Results of ways which consist of sandstone (from today):
– 98 ways with surface=paving_stones
– 2 ways with surface=stepping_stones

Unfortunately you can't add pictures here in changeset discussions, I could send you some from yesterday with sandstone paths/footways and steps. Or I could post them in the discussion https://community.openstreetmap.org/t/type-of-stone-in-surface-surface-granite-and-similar/9424. Should I do this?

Another note: I think the tag surface=sett will NEVER apply to a sandstone material, because sett stones are always made of of harder stone material (granite, basalt?). If sandstone, then the normal case is a "flat-machined sandstone PLATE" (larger plates or pieces of sandstone, while sett stones are normally much smaller stones). And at least here in my region you would never call a way with sandstone plates a "sett way", even if it's not 100% flat (but also the german translation of "paving stones" wouldn't be used with irregular formed sandstone plates, you would call it perhaps a "Sandsteinplattenweg" = "sandstone plates way", so I am not 100% happy with the tagging surface=paving_stones + paving_stones:material=sandstone. Here another value like surface=sandstone:plates – similar to concrete:plates – might be better in a semantic sense and easier to understand for mappers! IMHO.)

Perhaps this should have been taken into account before the mechanical edit took place ... 

And I saw the discussion on community.openstreetmap.org too late – for me it goes much too fast until facts are created and a mechanical edit with a bot takes place etc. But I'm also pretty slow at following discussions, I have to admit.