When you least expect a small wheel sighting, expect a small wheel sighting. Refilling my coffee cup in the 8th-floor kitchen when what to my wondering eyes should appear, but what seems to be a top-of-the-line raw lacquer titanium Brompton M6L with a hub generator, Brooks leather saddle, after-market leather frame protector, and Brompton cover bag. Wow, the works. But... what's with the walking?
Let's speculate. It could be an important call and the conscientious rider is wisely walking rather than attempting to talk and ride. Or, it could be a flat with a call for help. Speculating further, it could be a new bike with a pinch flat. Always deflate those tubes, massage the tire, and slowly re-inflate, to let the tube move into the correct position. Why the phone call instead of just making the change? Could be a rear flat, which, for someone unfamiliar with a Sturmey-Archer hub, presents a confusing scenario--how the heck do you get that darn wheel off of the bike? Internally-geared hubs are becoming more popular every day. Here's a link to one video and another video explaining flat repair with a three-speed hub. Watch them, give it a try, and save yourself that embarrassing phone call (not that that's what's happening here). And, do remember to pack a few disposable gloves in your repair kit. You'll be glad you did.