No, other way round :) It's infinite usually (in terms of calculating lighting etc), but for things like fog, Corona has to know what distance to consider it as being at. The enviro distance is what determines that - in other words, "technically this is at infinity, but for purposes of needing to know an actual distance e.g. for fog calculations, treat it as enviro distance"
Otherwise, the HDRI or Sky would always be "full fog" :)
(This is exactly what the enviro distance is for, so everything here is "working as designed")