I somewhat agree, I was thinking the same thing. I am troubled by the fact that both engines had the same thing happen at the same time.
It is obvious that the AAIB is also thinking this, but unless both engines are sourced off the same tank, both inlets getting clogged by ice at the same time are pretty slim.
It is likely that ice will be ruled the cause, simply because nothing else was found that could have caused it.
It still is damn strange.