Also prefixed by not an expert here; but know a few in the industry and somewhat keep up with it.
The push away from coal to other sources of power (combined with the closure of gigawatts of nuclear power) has put the network under more stress than it's been in the past few decades [1]. I'd expect more of this in the future in cases of multi generator failures; there just isn't that much in the way of generation to take up the slack.
Luckily we're in summer where demand is much lower, if this was to happen in winter the outcomes could have been much worse.
//edit - Just to be clear though, this does seem to be totally benign and could have happened to any other well equipped grid. A gigawatt of power dropping out in such a short space is going to result in some kind of load shedding. Denorwig spins up fast; but not that fast.