Hit-man Jun's inference was reasonable. But it was slightly inconsistent.
The Yin-Yang Escape was a wonderful evasive technique. So much so that even the Eight Great Masters couldn't find Jun Moxie's tracks. But the Yin-Yang Escape didn't use the five key elements for the time being. One could go into hiding, but they'd still be discoverable for they would weren't escaping into the void. The technique merely altered the flow of air to create this anomaly. This technique wasn't much of an anomaly from this perspective. In fact, it was quite ordinary. A person would basically be walking around with some alterations in the flow of air around their body.
The vast majority of people were unable to detect these subtle changes.
However, who was Lei Wubei? He wouldn't have been worthy of his name if he couldn't detect these changes.