For an outage this big hopefully they'll have some idea what happened, the initial rumblings sound like some sort of frequency stabilization event... so I'm guessing that's what the operators saw at least. You're right that they're a little gunshy saying something definitively I'm sure.
Unfortunately there's really three fundamental things working to destabilize Western power grids.
First was the move to wholesale power markets, whose primary "benefit" has been to take slack out of the system by pooling reliability margins over vast areas. The old balkanized system was more redundant, even if marginally less efficient.
Second has been wind and solar energy (and batteries). There are physical characteristics of these power sources that introduce more and varied failure modes (more transmission lines, intermittency, etc.). But there's also the physical complexity of managing them. The old bulk grid could basically be managed by guys calling each other on the phone and a few indicator lights on panels; the new bulk grid increasingly relies on advanced sensors and internet connections and predictive models that position the right resources at the right time to handle issues. If at the end of this we found out some new AI assistant misread sensor data and tricked operators into causing a ghost reliability event I would be only mildly surprised. Grid control isn't fully autonomous, but humans are increasingly in the middle of computer systems like Homer Simpson with the big red button.
Third is the electrification of the economy. Things like electric cars and heat pumps interact with the grid in ways we roughly understand, but we don't have backward performance data for and may not fully have stop gaps ready for. I also wouldn't be surprised entirely if we found out some major electric car or smart appliance manufacturer pushed an OTA update and accidentally caused a massive simultaneous power draw. I don't think there's that kind of penetration of those systems yet but it isn't out of the question.
It's an interesting time to be in the utility industry. This shit isn't going to get easier to manage in the near future, fuckups will happen as we navigate it. Have real disaster preparations on hand if you can afford it. Food you can eat unheated, a week of clean water to drink, and a camping toilet bag can be the difference between an unpleasant time and a scary one.