It's quite normal for cichlids to do this, just another example of their protective parenting behaviour. By keeping the eggs/fry in a pre-dug hole they are much easier for the mother to look after since they're are in a close proximity and tend not to leave the pit and the safety she offers until they are bigger.
You might notice some fish, my apistos for example, dig more than one hole sometimes and often move the fry from one of the pits to another. This is one of the reasons why it is preferable to keep certain cichlids in a tank with a sandy substrate, if there was to be a gravel bottom, they would find it impossible to do this.