Players conceding the game

[frogstar_A]

As I am not an old player here, I guess it was just to avoid them to lose more ranking.

That might have been the intent, but it doesn't work like that. Their ranking (and yours) was affected in exactly the same way as if the game had been finished.

I guessed the intention.. but I do not really get how we earn ranking points. So far I believed the more difference in points we have, the more points we earn (so other lose)?

No. The margin of victory is irrelevant. All that matters is the winners ELO / AES vs the loser

[Jellby]

Then check the FAQ for ELO (https://boardgamearena.com/faq?anchor=faq_account_elo) and Arena (https://boardgamearena.com/faq?anchor=faq_arena), depending on which ranking you mean. In any case, only the final win/loss/tie result counts, the score inside the game does not matter at all (except to determine the winner, of course).