What a strange way of doing things...
It's very confusing, yes. As shown here: 2011–12 Argentine Primera División season - Wikipedia, the free encyclopedia - Tigre just came second in the second 'championship' of that season, but if you scroll down, you'll see they also only just avoided relegation thanks to their poor form over the previous couple of seasons.
Theoretically, had a couple of results gone differently, Tigre could have won a championship and been relegated on the same day. Weird theory.
(better explanation from Tim Vickery's column here: BBC - Tim Vickery: Argentine title race is a sprint, relegation a marathon )