Hi-
It is likely from detonation, yes. The marks on the piston crown are typically "shiny pits", under illumination.
Not meaning to bore you nor insult, but when too much advance is in play, the air-fuel mix ignites BEFORE the spark plug fires and the normal burn begins (not the "explosion", as many say).
When the already burning and the spark-ignited flame fronts collide, there is often an audible metallic ringing sound (preignition then right behind it, detonation) which creates a sledge-hammer like shock to ALL the parts in the area: Piston Crown, Ring-Lands, Piston Pin, Head Gasket, Rods and Rod bearing.
That's what knock-sensors are supposed to prevent, but they are a LAST line of defense and can't react fast enough to prevent all disasters.
The TUNE can be a big part of it, as too much spark advace WILL cause any engine to detonate.
The OEM pistons aren't weak per se', BUT they won't tolerate much detonation at all. Forged pistons aren't immune either but they tend to fail over time and/or in a far less spectacular fashion.
I popped #8 on my own engine due to a tuner that thought could tune through our JTEC controllers as so many do, and me believing in his expertise.
That's why I'm now very particular on who does my tuning.
If more than one cylinder was also detonating (often the case with an aggressive tune), those pistons could very well be weakend. You can have them crack-checked but now would be the time to install some forged ones.
I was lucky as sometimes a chuck of piston will leave the cylinder through the Intake Valve and visit it's neighbours, jumping around like a crazed metal grasshopper continuing with more chaos and damage.
If your engine did pop a piston, make sure you check the valve and valve seats as stray metal can fuse itself to either surface. Assuming the valves didn't bend, a general lapping will restore the seal.
Piston damage can also cause a piston to no longer want to go up and down anymore and will exit out the side of the block, adding to the wreckage.
Hope your engine's injury is fixable.
Ronnie
