Well, some people use the terms interchangably so it's confusing. Just remember that title commitment has a specific meaning while preliminary title report does not.
Here's the TIRBOP definition of a title commitment:
“Commitment”, as used herein, is the agreement of an Insurer to issue its policy or policies of title insurance to a proposed Insured, as owner or mortgagee of an estate or interest in the land described therein, all subject to the provisions set forth in the Schedules and Conditions and Stipulations of said Commitment. The Commitment sets forth the requirements including payment of premium and Charges, that must be complied with prior to the issuance of the policy or policies.
So, a title commitment is like a mortgage approval or commitment letter, but it's for title insurance. It tells you the title insurance agent has approved the property for title insurance subject to certain conditions.
When someone uses the phrase "preliminary title report" they might mean title commitment or title abstract or even an attorney's opinion of title. So, when you hear someone use that phrase, ask them to be more specific.