The items are steps in a process, not an unordered list of rules.
Step 3 says if There are no DMARC records for the domain, check the organizational domain if different. Thus, step 4 is saying discard any non-v=DMARC1 records from the organizational domain.
If the From: domain has any v=DMARC1 records, we skip step 3 and step 4 is moot because of step 2 and we get to step 5.
If the From: domain has no v=DMARC1 records, we check the organizational domain if different per step 3 and then we get to steps 4 and 5