Most likely a 30mm round hitting it with all the small holes from the 'after effect frag' maybe from a oxygen tank or such. 20mm wouldn't do that much damage from internal pressure unless it hit something that would cause the frag.
I wonder about the size though as he says 'two men could fit in it'? Is he talking where the wing meets the main body? Wish we could see a picture, those things are a sight to see being able to land with all the damage they sometimes took.
