Abstraction? Judging by the jubilee clip connected to what looks like T+E.
Plenty of scope for a high resistance, high current connection to generate lots of heat thus precipitating the failure. Where's the neutral? Is that the remains of it on the second, more squashed looking jubilee clip at the bottom? But then again, what's going on with the wire to the neutral block at top right?
ETA: I wonder if it's the lower jubilee clip connected to the neutral being hard up against the phase conductor, in time rubbing through the paper insulation and causing the short circuit. I'd somehow expect the damage to be greater though.
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