Police said he escaped when the impact of the collision – which sliced off the roof – sent him flying into the stairwell leaving him suffering only minor injury.
The driver and another three passengers on the Go Bananas bus – which caters for stag and hen parties – also escaped injury.
However the road was blocked for several hours following the collision which happened at around 2.20pm.
Train services on the main rail line between Glasgow and Haymarket were also disrupted for a time while safety checks were carried out an investigation got underway.
A spokeswoman for Go Bananas confirmed their vehicle had been involved, but added: “To be honest, we’re still getting details of what happened.”
Lothian and Borders Police said they were still investigating the incident.