It's not particularly strange behavior for a suicide terrorist. Some folks in this fallen world think that their one-way ticket to paradise is to strap on a shrapnel bomb and kill as many infidels as possible when they blow themselves up. It's not a stretch of the imagination to think that the same sort of people would try it with a biological weapon.
I believe that is exactly what this Liberian man did—intentionally fly to the United States with the intent of infecting as many people as he possibly could. A walking, talking biological bomb.