Back to the original question-
Gushing can be from-
2 too much sugar
3 bottling before fermentation is complete, this is why bottling, or dong anything like racking to a secondary, should be done based on HYDROMETER readings and NOT the instruction or a calendar, or airlock bubbling stopping or slowing down.
4 Not chilling the beer and letting the co2 be pulled into solution.
5 Opening the bottles too soon, usually around 1 week, when the co2 is in the headspace but NOT in solution. This is best illustrated by Poindexter's video from my bottling blog.
6) Shaking/agitating the bottle.
These are pretty much the only reasons why a bottle would gush.