Unintended eating from tins is back happening? Not at home (10)

I believe the answer is:

snaccident

'unintended eating' is the definition.
(a 'snack accident')

'tins is back happening? not at home' is the wordplay.
I cannot really understand how this works, but
'happening?' could be 'accident' (accident is a kind of happening) and 'accident' is present in the answer.
This may be the basis of clue (or it may be nonsense).

'from' is the link.

I've seen this clue in The Guardian.

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