Could've just plopped it down in a place where there is some other, more immediate distraction around. Hot chick on a sign becomes visible at just that spot, etc...
Remember in magic a major element of the trick is distraction. You won't see the slight if you're being misdirected somewhere else...
I think you're right. And there might be another contributing factor; consider what you'd be doing walking in one of the busiest pedestrian intersections in London. I don't know about you but I'd be looking at pedestrians to avoid running into some random person walking in a direction I wasn't expecting - not down at the ground. The circle he drew around the wallet seems to be for no other reason than to make the audience believe that the circle is significant.
James