Thanks. Your quotes are not about the Alto system software. The Star paper is about Star (1981) and itself warns that people "wrongly believe that Star was written in Smalltalk"; your first Sweet quote credits Tajo's window contexts to Lisp property lists, not Smalltalk.

The Alto OS, Bravo (1974) and Gypsy (1975) were written in BCPL by CSL/POLOS people (Lampson, Sproull, Simonyi, Tesler, Mott); the June 1975 Alto OS manual and Alto Packages contain nothing from Smalltalk, and they had no overlapping windows or pop-up menus.

Mesa the language (MPS 1971, named 1974, self-hosting 1976) owes nothing to Smalltalk either. Sweet's "patterned after those of Smalltalk [Kay76]" refers to the Dec 1976 Mesa 1.0 debugger's optional, "experimental" window manager. It never touched compiler, binder or OS and was dropped/replaced in Mesa 4.0.

Smalltalk influence is documented for Star and for Cedar's environment goals, both 1980s. For the Alto software of 1973–75 there is none; for Mesa 1976–77 it is BitBlt plus an experimental debugger add-on. BitBlt and overlapping windows were specifically Ingalls' work, which he internally demonstrated in 1975.

Paul McJones has a nice Mesa History Collection with a lot of primary sources from the time: https://softwarepreservation.computerhistory.org/mesa