At least this message is harmless, they just copied that over from the Fairphone OS script and didn’t change it. The script will also say it installed Fairphone OS in the end, which isn’t true.
That’s confusing for sure, but only a cosmetic issue, not a functional one.
However, the switcher installation sometimes doesn’t seem to work according to earlier reports here in the forum.
Alternatives:
Download the “Manual installation” file (not the switcher) from https://code.fairphone.com/projects/fp-osos/user/fairphone-open-source-os-downloads.html and use this manual file instead of the Fairphone OS version with this guide …
Or use this guide for an install from scratch …