It doesn’t always have to have a minor 7th chord in front of it. So if you see a 7th chord which is a tone below the chord it resolves to, that is a backdoor cadence. This is just as common as seeing this with it’s II chord which would be Ebmin in this case. In this case the Ab7 is the backdoor leading to Bb major. Finally, I leave you with an example of a backdoor progression without it’s II chord preceding it.
