MOST players don't make the Weekend Round. In fact, 60-75% of tournament entrants do not make the Weekend Round. If you manage to finish in 50th place in your Weekend Round: you're actually in the top 15-20% of ALL players that entered in that Skill Tier.

This as a one off would not be enough to earn you a promotion to a higher Skill Tier, however if you have previous good tournament results, or are consistently beating ~80% of your opponents in this way, then you'll rightfully earn a place in a higher Skill Tier (as will other players that are having similar or better success).