Looks like you get bitten by that Metabase is “clever” and sees it’s a date type so it displays the time dimension as dates - in Metabases standard date format. (Americans don’t care much for week numbers). Maybe as a work-around you can cast it to a text type?
Improvements for the X axis labels have been added to the next upcoming major release 0.29 wheneven it’s ready:
Added to corresponding github issue #7236, apparently it’s regular numbers too not just dates that can be interpreted by Metabase as a regular date. Concatenating a special character at the beginning of the category label solved the problem in this particular case.