Facebook chat order basis?

[Nobody]

Why does this specific person on the upper part of my chat box keeps on climbing on the top of the list? just curious.

When he goes online, he starts on the second to the last name on the upper part of my chat box then after few minutes he's the 5th from the top, then second... does the name on the chat box has basis? why is he climbing up?

I just noticed that the names on the upper part of my online chat box are the people I'm close with (we exchange messages, likes posts and pictures and gives comment) except for this specific guy who I've never even chat with and recently added, like 4 days ago.

Anyway, I'm just curious and I heard that the people on the upper part of the chat box (before the more friends) are the ones you usually interact with or who visits your profile regularly... is this true?

[Jack]

Ordered by name.