To be fair, when sending a Pixel for reparations, Google very clearly and explicitly asks to factory_reset the phone.
I personally didn't reset it when I sent my Pixel 3 to fix the charging port because my Pixel was fully encrypted.
All Pixels are encrypted by default as long as you have any kind of lock method enabled (PIN, password, shape...).
I don't really understand how this person got his files in cleartext and accessible.