Can a company offer someone an interview and 3 hours later say the position is filled?

There's nothing unlawful about canceling an interview as long as it was not cancelled based on unlawful criteria.

Sure. The initial representative might have been mistaken, or the position might have been filled in the interim, or someone in the company decided the employee did not fit the needs and did not want to waste their time with an interview that would have been meaningless. There are lots of reasons why a company could do this. There is no legal duty placed upon an employer to follow through with an interview just because one company representative offered one. Sorry.

Yes, there is no requirement that the employer interview you.