Blackbird incubating egg in plant pot (1 Viewer)

I understand that it's not too unusual for birds to "drop an egg" outside the nest and in unsuitable places (but can't find references to the habit - suggestions?). Yesterday, I was shown a single Blackbird's egg in a plant pot laid on the bare fibrous compost material without any preparation (other than a very shallow hollow). I assumed the egg had been abandoned but to my surprise, as I moved away a female Blackbird scurried up and sat tight on the egg. Further enquiries revealed that the bird had been incubating the egg for at least two hours (although the egg was reportedly cold). How unusual is it for an egg to be laid in this manner and then incubated? Again any references would be useful.

I'd guess the bird considered the potting compost was already suitably soft to act as a nest?

Problem is going to come with any heavy rain, or when someone wants to water the plant.

To my astonishment, the single egg hatched on Saturday and the chick has survived until today. Any ideas how unusual this is? I can't find any references ...