the theorists are saying something more subtle happened. Either of:
a) A coup-credible general or two or three, would have been bribed to trigger it, so that Erdogan could identify his enemies red-handed. The rest of the plotters in the army would have been under the impression a real coup was happening. This would explain the quick surrender of the bridge soldiers without a fight, because the horrible reality that they had been duped would have dawned upon them.
Or possibly more likely:
b) Noises and rumours were discretely circulated by his agents that Erdogan was preparing a large purge. This is credible because it is reported the list of all the 3000 judge firings, for example, was pre-prepared (as you would expect with such a large number). Tactical leaks to the right people of would have forced an immature half-baked coup plan hastily and prematurely to be executed, in panic and to protect themselves pre-emptively from said purge. This is the scenario where Erdogan basically raised the stakes in order to call their bluff, and thus flushed his enemies out into the open.
Personally I find the consequences of this "coup" to be much too neatly convenient for Erdogan, the purge too pre-meditated in appearance and logistically well organised, for the finger of prime suspicion not to point directly at him.