VEI of 0.5 is 0.0001 km3 ejecta, not 0.00001 km3.Scale is logarithmic (powers of 10), see official USGS VEI scale.
File is correct. The logarithmic scale applies after VEI of 2. See The Volcanic Explosivity Index (VEI): An Estimate of Explosive Magnitude for Historical Volcanism, Newhall and Self 1982.