Those pistons look like someone put Comet in your oil
The only motors that I have seen that failed from a lean mixture are dirt track or other race car engines. I just haven't had a lot of experience with street motors failing.
Usually, what happens with race engines is they hole a piston, or the center of the piston "sinks" This is usually from very high compression, heat, and a lean condition. Detonation heats the piston and the material gets soft. Then the pounding from more detonation pushes the piston top downwards. In most cases, the engine holes the piston before the problem is noticed, but in a few cases, the sunken piston will be caught before total failure.
What you have there is interesting and I hope some others chime in with their thoughts.
How lean were you running? Did you see evidence in other areas, such as hard cranking when hot, or with excessive blueing of the header pipes?
I wonder if detonation led to ring failure which then scarred up the walls...?
Please share what you can because I do NOT want my pistons to wind up like that. I am running pretty lean on my 750 right now.
If your bike was lean enough to do that, you should have been getting great gas mileage. What kind of mpg were you recording?