I am doing the challenge for https://trailhead.salesforce.com/content/learn/modules/business_process_automation/process_builder# and I created a process builder for this. In "immediate actions", I could see contact object fields. I was looking for AccountId in this list. But to my surprise, I could just see the account number. Where does this account number (and for same reason) other fields from this dropdown come from? I don't have Account Number as a field on Contact object and this dropdown should be showing fields from the contact fields ideally. Please see below image which speaks my try.
EDIT- This is what the dropdown list has and these are the fields at contact object. I agree that I have account number in contact object but then there are many other discrepancies in these two tables.