It sounds like the hiring manager jumped the gun. He probably offered you the job before discussing it with senior officials and was told that they wanted other people to be interviewed.

Some companies mandate that a specific number of candidates be interviewed and assessed before a job offer can be made and maybe the hiring manager didn't follow that protocol. Maybe he only interviewed 4 candidates instead of 5.

There are some positions that require more than one interview because the "higher-ups" want to be included even though they don't have any say in who actually gets hired and/or are not even going to be working directly with you. It's mainly a power thing.

You mentioned that the hiring manager stated references needed to be checked. That is something else he may have forgotten aobut or neglected to do and then got caught.

Since no papers were signed stating any details regarding the offer and acceptance of employment, nor did you discuss any specific start date, the offer can be rescinded at any time.

Remember, as well, that most states are "right to work" which means that the company has the authority to hire who they want, fire who they want, rescind any job offer when they want and the individual has the right to not accept any job offer, rescind their acceptance, quit when they want. Notice is not mandatory in right to work situations.

Is what this hiring manger did proper and professional? H3ll no.

Is it legal? Unfortunately, Yes.