There were common style elements across all the Xerox PARC software systems, the one not mentioned so far is Interlisp-D. I don't think you can claim that Wirth was only influenced by the BCPL and Mesa group.
I just repeat what he said and wrote. You can have a look yourself at the Oberon System, see e.g. https://github.com/rochus-keller/OberonSystem. Not quite similar, isn't it? Wirth didn't like overlapping windows.
As he writes he was influenced by the Mesa language when he developed Modula-2/Lilith and by Cedar when he implemented Oberon/Ceres.
In fact, Mesa and Mesa/Cedar developers explicitly refer to their goal to replicate Smalltalk and Interlisp-D developer experiences on XDE and Cedar, across their papers.
