Let's refer to this handy chart.
Dash (PHB 192), Disengage (PHB 192), Dodge (PHB 192), Ready (PHB 193), and Cast a Spell (PHB 192) are all Actions. You get to use one of those per turn during ordinary cases. Note that Turn Undead is an Action.
The only Reactions possible are an Opportunity Attack (PHB 195), a Readied Action (PHB 193, must have used Ready on their most recent turn), or a Cast (PHB 192) spell that has a casting time of a Reaction. You get at most one of these a round (so, it is refreshed only when their initiative comes up).
Bonus Actions can be an Offhand Attack (PHB 192,194-195), when using the Two-Weapon Fighting rule, a Cast (PHB 192) spell that has a casting time of one Bonus Action, or a Class Feature (PHB, see specific Class Features) with a time of Bonus Action. You get one Bonus Action per turn.
So, given this information, it appears that your intrepid Cleric took three Actions in a single turn. Short of any Class Feature or Racial Feature that might provide an explanation for this, this was definitely an abuse of the action economy.
To be sure though, check to see if they're using a particular Race, Feat, or Class Feature that might have allowed this action economy. I'm not aware of any such items that would match this, since action economy is tightly regulated to avoid the sort of balance problems you witnessed in that encounter.
The Cleric could probably still have won, but it would be a lot more challenging. Turn Undead on one, hopefully kill the other within 10 rounds, do some healing, if possible, then deal with the other. Or, use every single Action to Dash in the opposite direction to safety, whatever that might mean.
It'd be worth your time to reread the rules and refresh your memory, and maybe even find a handy chart like the one I've linked for moments like this. Also, whenever a player does something that seems genuinely Too Good To Be True, it never hurts to double-check the rules, just in case.