As Abel says, it's not usually a case of the lume being dirty that causes the discolouration, it's wholesale chemical change. And it doesn't entirely look like the lume has been removed, because, looking closely, areas that were free of lume before (the top of the '1' in '12', the bottom left of the 8 and 11 o'clock markers) still stand out differently from the lumed areas.

Perhaps it's a trade secret of that particular restorer, but I'm struggling to think of how to do it either mechanically or chemically once the lume is as aged as it is in the before photos, so now I'm itching to know how!