Is AUTHOR wrong in the post ? POST : A lot has happened at work recently. Here's some background:
On a Friday, the entire company was informed a specific branch was closing. It was a small office of only 10 people but one of them "G" did the most important job for my 10 person department at the main office. 
This was news to my manager who was technically G's supervisor. 
Cue some frantic scrambling the following Monday which was cut short by a company wide tech issue that afternoon. Who would take over G's job was still a priority but it seemed like it was put aside for the time being.

That Wednesday I was unexpectedly offered G's job by our manager with supervisor present. I officially accepted Thursday morning. This wasn't an open position and I wasn't anticipating the offer. I was happy with my current job and left it up to my superiors to decide who could fill the role.
On Friday I hear my coworker "S" talking about asking our manager for G's job, S had scheduled a meeting already and was asking for tips on how to secure the position. He mentioned he wanted to go through all his recent accomplishments before actually asking for the job.
I was technically eavesdropping but there had already been a couple opportunities for my supervisor or manager to announce my promotion to our department. They hadn't and figured it was for a good reason so I didn't want to announce it myself. 
I texted my supervisor to ask if I could tell S he should cancel but she was in a meeting and didn't reply in time.
S spent an hour with our manager marketing himself and trying to get the job.

Come Monday and I am announced as the recipient of this promotion. Ever since S has been acting weird around me and so have the other couple coworkers he had told about wanting that promotion. 

I didn't ask for this promotion but telling him that won't help, S is absolutely qualified for this promotion but for whatever reason I received the offer. I wanted to tell him before he spent the time to present his case but I didn't trust him to keep it to himself so I wanted explicit permission first. I'm honestly not sure if he knows I had the job before it was announced or if he thinks I tried for it too.

AITA for letting him spend time on "applying" for a promotion I already had?