Tournament standings:
https://boardgamearena.com/tournament?i ... ge_display
Under Match 2, game #18, xorsyst_uk (player #87,850,895) and AbCdEfGhIj12345
384 (player #92,900,255) tied, both awarded 1st on the game page:
https://boardgamearena.com/table?table= ... 35&nr=true
So OP's question is very good, why did AbCdEfGhIj12345 advance to Match 3, game #9:
https://boardgamearena.com/table?table= ... 22&nr=true
I assume that the player id's are conferred sequentially by account creation date, so xorsyst_uk has the earlier creation date. We can say for certain that the rule here is
not that the older account advances.
In this thread from February 2023, a player was told was told by BGA support that the tie-breaker for a round-robin tournament (in a game with no scores) is random selection:
viewtopic.php?t=29137#p136657
The OP here (xorsyst_uk) is asking about a single-elimination tournament (not round-robin) but it does appear quite possible that the determiner of who advances was made by random selection between xorsyst_uk and AbCdEfGhIj12345.
See also this thread, and particularly the post by radicarian:
viewtopic.php?t=17794
And here's another thread on the same topic:
viewtopic.php?t=29618 referring to this table:
https://boardgamearena.com/table?table= ... 77&nr=true