It depends on what you mean by "hard coded". There's no html or css in the php code.
I don't know much about doing that kind of thing, but there's this article:
https://vborg.vbsupport.ru/showthread.php?t=228484 It's about two-column forums and not threads, but it might be useful. But it does go across rows then down, as opposed to down one column then down the next. To do that you'd have to do some php coding (for threads I think it would be in forumdisplay.php).