Yes the Back Garden is the feature on the ground and Concrete Garden operate the previously described project (visible in the Bing background layer) from it, although their office is based elsewhere. The details on node/3004928033 look to be accurate, unless you feel the address should be noted as a correspondence address (and not that of the feature itself), and the landuse should be garden or allotment (it's technically both) rather than grass (as it was before creation of the community garden).