In my opinion, the mistake black made was not on move 4, but on move 2.
Try Nc6 next time.
jk, of course, about the mistake.
But why?
It was annihilation.
The best that can be said is fair play to feldmm1 for chancing the move! Perhaps there is a lesson for more experienced players here, take a chance, you never know what might happen :-)
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