I think you misunderstand the post. Different contaminants have different boiling points, many of which are lower than that of water (100*C/212*F).

In a closed system, many industrial pollutants will vaporize at lower temperatures than water, to be collected and condensed by the condensing coils and wind up deposited with your supposedly "purified" water in the collection container. So while you've eliminated those contaminants that have a HIGER boiling point than water, you still have those with a LOWER boiling point in your distilled water. And the majority of industrial solvents have a lower boiling point than water.

This could be accommodated by starting the distillation process with an open container to avoid collecting the more volatile contaminants until they have boiled-off, then sealing the system to complete your water purification cycle. The question that nobody seems to be able to answer is how long does this uncollected boil need to last for a given quantity of water to be effective. My guess is there's no fixed answer, it depends on what's present and in what quantities. If your collected water contains a large amount of a chemical with just slightly below 100*C boiling point, perhaps it would be impossible to effectively distill potable water.