What Does It Mean When an Employer Uploads The Position I Just Interviewed For?

It could be another position of the same job. They might not think any of the current candidates are stellar and are hoping to attract more applicants before making a decision. There are many possibilities. As to whether you should be worried, there was never any promise you would get hired, so the re-posting of a position really is immaterial. If you're the best candidate you'll get the job. If you're not the best candidate you won't get it. That's really all that matters.

They may have already made a decision...a decision to not hire you or any of the other candidates that they already interviewed. That isn't lying in any way.

Or, it may be an automated posting.

Or, they may have multiple positions to fill.

Or, an HR person out of the loop of the interviewing process might have posted the job by mistake.

Regardless, you should never assume you have the job until you get an offer. Keep up with your job hunting up until you get the offer in hand that you want.

It may have just been automatically posted again because the position is still open. They may want to see more candidates. The reasons are endless.

Why would they lie? Maybe another position has become available.