When a horses eat with a bridle does it cause colic?

No, eating anything with a bridle on will not cause colic. Typically horses are not allowed to eat while wearing their bridles because it is a bad habit and the bridle is supposed to mean that the horse has to work and not eat. However if the horse is not working and is resting a mouthful of hay or grass will not harm them, but it can make the bit dirty which will require extra cleaning.