I am afraid that you will never know the answer. At least, from your description, there is no obvious cause for failure, and there is just no way to guess what exactly went wrong this one time. The recipe and your process seem fine and should work in principle.

Typical causes can be:

• You didn't wait enough. You say you only waited for 90 minutes - yeast doughs can easily need more, and I would wait for at least 6-8 hours before I pronounce a yeast dough dead. While this shouldn't be the case at 30 C, your estimation for your oven's temperature at this setting might be wrong. Or maybe the dial was visibly turned to this setting, but due to some mechanical problem, the oven didn't actually turn on.
• The opposite of my last sentence may have happened - maybe the oven turned on to one setting higher, and you warmed the dough enough to kill the yeast.
• You may have been distracted and made a wrong measurement without noticing.

If you are accustomed to high-hydration doughs, then this dough can be expected to feel on the dry side for you, it is at 60% hydration. Or maybe the original recipe assumes that people will proof the live yeast in some water additionally to what the recipe calls for.

The "stiff" part is likely because you apparently kneaded it for exactly one interval of 12 minutes with a stand mixer. You should have let it relax when you saw it becoming stiff. Also, consider transitioning from kneading for some amount of time to recognizing what properly kneaded dough looks like and stopping when it's done.

Anyway, neither the low hydration nor the unrelaxed gluten should interfere with rising. You eithr made a mistake (wrong measurement, wrong temperature or waited too short a time as explained above) or it was some weird fluke, these happen too.

It could be that his posted amounts of liquid are incorrect. When looking up various croissant recipes online, I see ranges of 280 grams of liquid (the lowest I found) to 360 grams for 500 grams of flour. ...and that is just with some cursory searching. His indicates 250 grams, and while that is a small difference between his and the "driest" recipe I quickly found, with the additional sugar, that might account for your dry dough. I would say that if you immediately felt it needed more liquid, your hunch was probably correct, and you might want to cross-reference this recipe with several others that are easily accessible with a quick on-line search.