Yes, it's confirmed that Yetis drop Bunnyslippers. I wanted to paste a helpful quote with screenshot thanks to my source, Tibia Bosses: The Legend of the Yeti "It happened on Isle of Merriment, during the last day of Test Server for the Winter Update 2019 (November 18, 2019). There was a regular yeti spawn which could be camped. Hunter of Dragoes and Lee Kun killed about 112 yetis in 6 hours and Hunter was the one who looted the legendary item. Congratulations from Tibiabosses staff and thanks for sharing the great news!"
Source of information/screenshots: Tibia Bosses: The Legend of the Yeti
https://www.tibiabosses.com/forum/topic/the-legend-of-yeti/
There is this topic on tibiabosses which people discuss about it, but there are no valid and not faked screenshots or videos proving that someone has looted them.
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