Rival

Awarded per battlegroup at the end of a season based on top ranked percentage.

0.0% - 0.5%: Gladiator
0.5% - 3%: Duelist
3% - 10%: Rival
10% - 35%: Challenger

Before Battle for Azeroth, this title was released based on a certain percentage of players who participated in arena. If you were in the top 3-10% with 50 3v3 arena wins in that season, you were presented with Rival: the FoS pertaining to that season and a temporary title for the following season. However, in BFA, this system is receiving a massive overhaul. Players will now enter a formal bracket based on their seasonal rating:

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• Combatant: 1400–1599
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• Challenger: 1600–1799
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• Rival: 1800–2099
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• Duelist: 2100–2399
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• Gladiator: 2400
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Quoting the article, they are still working out how to distribute end of season rewards (which includes the titles listed for the brackets above). This means that titles underneath the Rank 1 Gladiator are still being worked out, and according to the article:

We’re still in the process of working out the possible end-of-season rewards, but for now we can say we’ll be keeping the special seasonal Gladiator titles for the very top players at the end of each season. Those who get the Gladiator title will also need to win an additional number of games to earn the mount as their reward.

Here is the official rating update posted by Blizzard.

You were probally drunk when you saw a level 70 with this title, it changed is level to 67