Well, MM was called an “arcade adventure”, which seemed be a whole genre that was not getting a lot of releases back in 1987, according to this review in Zzap!64
https://archive.org/stream/zzap64-magazine-032/ZZap_64_Issue_032_1987_Dec#page/n12/mode/1up
And Zak was called an "action/adventure game"
http://archive.org/stream/zzap64-magazine-047/ZZap_64_Issue_047_1989_Mar#page/n69/mode/1up
Of course having to drive the cursor around using a joystick was a lot of arcade action right there!
By the time Indy3 rolled around, they mentioned “pointing and clicking”, but not yet as a description of the game genre.
https://archive.org/details/zzap64-magazine-057
(Page 40)
This 1990 review of MI mentions “point-and-click” . Still not adventure in the same sentense. (Although synonymous to Lucasfilm games)
Anyway, does it really matter who coined it and when? Who cares?
Oh… @RonGilbert does…