Haloumi cheese is very hard
The cheese failing to rise and being hard are definitely related, but it's more likely that there was a problem in the cheese chemistry (particularly, in the culture), than cooking it longer in the whey would have helped.  In other words, the most likely problem culprit is your starter/culture being poor quality or somehow added improperly.  You are using non-chlorinated water, correct?

This is, of course, assuming that you followed Carroll's recipe exactly.  If you cooked the curds at too high of a temperature, or for too long, or if you re-cooked the cheese in the whey at too low of a temperature, those would also cause similar problems.

While it's not uncommon to need to cook halloumi in the whey for longer than expected (for example, see Gavin Webber's cow-milk Halloumi video; he has to cook it for twice as long as the recipe specifies), Carroll's cooking time of an hour is already very long for finishing the cheese.  Other recipes specify more like 15 minutes to 1/2 hour.