Depends on how you intend to use the photo.
Alamy is out of the UK, although they have a US office; their information seems to be what they do on their site but not necessarily what is done otherwise in the US so that info. in the link above may not apply to your situation. Try looking at
American Society of Media Photographers or PPA or other professional photographers organizations for guidelines. ASMP has a pocket release to carry with you and an app.
Alamy sells worldwide so their releases HAVE to conform to the most rigorous standards. Model releases are not normally required in the UK but in practice you'll never sell an image or get it accepted by a stock agency without one that conforms.
Usually the guideline is if the person (or property) is recognizable. To me if I knew this person and saw the picture, I think I'd know who it is. If you live in the area and use it locally I suppose someone could see it and recognize the person.
I bow to your superior eyesight.
Where I live broadband is slow at time so I couldn't look at the full size image without waiting half an hour for it to load.
In the future, if you think you may use a photo other than personal use you might need to think about getting a release signed at the time. Or move around a little and change your vantage point and keep the person/people out of the pictures if you're photographing landscape or scenery. This may or may not be a public place; if it's in a park for example it could be under policies of the park district regarding camera use, etc. and you might need to look at the website for the park.
Agencies would take them for editorial, as you said. Sometimes when you get a shot like this you don't have the time to move enough to get the shot or by moving the shot is lost. In these cases, if you can't get the release you just keep the shot as fine art (or editorial, or for personal boasting) and wait for the next time... there will be a next time if you are patient and have your camera with you.