There are plenty of examples of New Testament Warriors.
I strongly suspect this is a volume issue not really a prayer issue.
If they were in a circle giving “power walking instructions” (we are going as far as X store and then to Y store 3 times) in a loud disruptive manner then it would be the same issue.
The guard SHOULD have just said, we have volume rules and please keep your group at low volume, this would not be an issue.