I'm not trained to analysis debris from pictures, but common sense suggest those are shrapnel holes to me.
The key is less the holes themselves, but more everything else.
There are clearly a large number of scratches and dints and near perforations that all form too clear a pattern and are too numerous to have been caused by ground impact IMO, especially the kind of soft grassy fields the debris came down in.
If those dints and scrtahes were caused by the same thing that punctured the fuselage and caused those holes, then it clearly could not have been cannon fire as that metal hull is nowhere near strong enough to deflect cannon fire like that.
The only thing I know of that will release a large profusion of debris of varying sizes, all traveling in the same general direction, with some having enough mass and energy penetrate an airplane fuselage while others can only scratch it or dint it would be a fragmentation warhead from a missile.