Possibly. Or 'why did your fuel readings deviate from what was actually in the tanks' or 'why did we leave with less fuel than we thought we did' and so on. There are so many variables here speculation is completely pointless. All we know is that something went wrong, that it almost led to a crash and that it involves an airline with a very good record when it comes to things like this.

Low fuel happens, but this is (very) exceptional.

I don't know. As the parent said, I'd be careful with guessing the root cause right now. They should not have been this low even if diverted due to weather.

By asking such a question you understand the need for an investigation