Many thanks to @DiabloNYC for sharing his blog post and to Ayako for tweeting the link!
@DiabloNYC saw Keanu sitting on the loading dock on his birthday back on September 2, 2010. He approached him for a selfie for his wife who is a Reeves fan. During the encounter a paparazzo was shooting them with a teleoscopic lens from a car. Back in 2010 the photo was picked up by many of the celebrity sites. Now we have the story behind it. The photo and short account is here.