Last time I saw an open foot on a very similar vase it was part of a garniture - a three piece set for displaying on top of the cabinet. As there is no function intended, it does not matter if it has no bottom. The middle part of the garniture usually has a lid. On the particular set I saw, the lid was fixed - blown vase and lid all into a single mould, and open at the bottom. Bohemian end of the 19th ct. of course. Not saying this one is too - just offering an explanation for bare bottoms.
The other thing to try is turn it upside down and contemplate a candle....