You are right, that is a large part of it, but WHY is it that primarily Christian nations have developed the agriculture technology and processes to create such surpluses.
In times past as we were developing our agricultural abilites we would build churches as the one of the first most important buildings (before government buildings) in farm areas.
The church was at the center of those societies which flourished well ahead of non-Christian socieites.
Most non-Christian nations still can't figure out how to get the agriculture right because they do not have the cultural values necessary, in part. The other is that we are blessed by God.