The Blood Thirsty challenge aims to get you to level *more* through killing instead of questing. Questing is sometimes necessary to access some content and we also need to accommodate folks having completed account-wide pet battle quests: these count against even your newly created level 1 character.
Currently the quest cap is 300 for all classes except Death Knights, which is 135.
The change will set the quest cap at 150 for ALL classes starting June 1 at Midnight Pacific.
Characters that are listed on the site before June 1 will be held to the old standard (ie. grand-fathered in).