Yeah, I think that it is the most likely explanation, however there are a lot of questions which hold me off being absolutely sure, the descent spiral just before the plunge into the sea and the fact that it took off from Charles de Gaulle airport and headed towards Egypt rather than the other way around.
Given that France has received two terror attacks and there's been an attack on a European airport fairly recently you'd expect security to be pretty tight at Charles de Gaulle.
The descent spiral, as shown in this Beeb graphic:
seem as though perhaps someone was still trying to keep control of it, however it's equally just possible that this was just the way the wind was affecting the aircrafts glide path as it descended out of control.
Sadly terrorism is the most likely option, although it is strange that no-one has claimed responsibility for it yet, normally Daesh and their ilk are all over something like this but they've been quiet, I guess it's possible that they're holding back while their operative gets clear, but who can say?
Either which way, a very tragic day.