The Wikipedia article is incorrect, Monero still uses ring signatures. Bulletproofs are used as efficient range proofs in RingCT to hide the amount in transactions.
https://www.getmonero.org/2017/12/07/Monero-Compatible-Bulle...
https://www.getmonero.org/2017/12/07/Monero-Compatible-Bulle...
Thank you! There's a lot of difficult-to-google info locked up in comments like this, and I truly appreciate the effort spent replying to randos like me :)