How to know if you are on a waiting list?

I had a final interview two weeks ago for an analyst position at a REPE firm. Last Wednesday morning, the hiring manager asked to give me a call and told me it is down to me and another candidate - during the same call the hiring manager said they would try to find another role for the candidate they don't choose, but he's not completely sure if it is possible yet. He said to move the process along faster, it would be useful for me to tell him salary expectations and the earliest I can start.

Two days ago he reached out to me saying that he didn't want to leave me hanging, but they're still having internal discussions and he is hoping he will get back to me soon. I know the team he is on is understaffed, but I'm not sure why it's taking so long to choose - I feel like everyone kind of knows who they want to hire.

The whole interview process was really quick until last week - they seemed to have gone through and weed out all their candidates in just a few weeks prior to last week, so I don't know why it's taken them almost a week and a half to narrow down between me and the other candidate - I'm beginning to feel like they chose the other, and are either waiting for a response from him/her or he/she already accepted and they're waiting to see if they can find another spot for me.

Am I overthinking? Or do my theories sound about right?