SOME of the building may have been blown outwards: the result of overpressures and shock waves bouncing off interior walls, other buildings, and so on. But the ORIGINAL shock wave and overpressure came from the EXTERIOR of the building -- there were no charges inside (apart from a few pistol cartridges, etc. from the FBI and building guards).

And I find "Hustler" to be such an unimpeachable source that I'll believe it without even bothering to find an issue.