I saw this scene out of the corner of my eye on my bike ride to work this morning; it was in my field of vision for approximately 3 or 4 seconds, which made for an interesting challenge.
Usually when I get the idea to do a memory sketch (when I see something cool and don't have a sketchbook handy), I take a moment to observe my subject intently for as long as I can, so as to try and pick up specific details that I'll be able to recall when I sit down to draw it. With this drawing, having 3 seconds of peripheral information means that probably a lot of what wound up on the page is stuff I made up. I mean, for all we know it could have been a lady drinking a latte shooing a squirrel that I saw. But that's the fun of doing this kind of drawing, I suppose.
Give it a shot sometime! Next time you find yourself thinking, 'that would be cool to draw,' stop looking and start making things up, just for a change.