What a fun weird setup. 7-speed cassettes still exist and are available. 7s freehubs not so much - instead the narrower cassette is mounted on the 8s freehub with a spacer. My BIL's recent Trek 3700 was built this way. Good upgrade for a 7s bike with a broken axle.
All kinds of fun combinations of shifters and cassettes are possible, as per
this article and
this article. Remember if you got 9 clicks then it's a 10 speed.