How is the instance decided?

In the screenshot you can see several posts from the same community shown as coming through two logged in accounts. Does it just randomly choose which account, first come first displayed, something else?

The idea behind multiple accounts is so my feed remains mostly usable when an instance goes down. The first one I signed up to (lemmy.one) went down after it upgraded and hasn't yet come back, the second one has been up and down (lemmy.world) and I decided to sign up to 4 total for redundancy, and because eventually there will be a way to tie the accounts together in a cohesive way.