I was also a bit confused by this. I thought the standard notation was round brackets, but maybe doesn't work well in ASCII?

Round brackets are standard in the US but that notation is used in France and some other places.

  (0, 1)
Is this an twice-open interval or a 2D vector?

See, this is why Bourbaki introduced the ]0,1[ notation.

Is there any reasonable situation where you'd be confusing a vector with an interval? Having done mathematical writing and grading of tests using both styles of notation (simply adapting to what was used at the institution), I can't say that I ever noticed any practical difference between them.