Board Game Arena

My buddy just played in a 3 player game where two players tied in first (https://boardgamearena.com/table?table=509221874) but he lost ELO.

Why is this the case? How is the gain/loss of ELO calculated?

Because elo is an evaluation of skill, not a prize/reward for winning. If you tie with a player of lower ranking, your elo decreases, because you were supposed to win (on average).

https://boardgamearena.com/faq?anchor=faq_account_elo

Thanks!