The Yakuza series is known for its confusing naming conventions but it seems even the developer gets mixed up, as Like a Dragon Gaiden: The Man Who Erased His Name features a tutorial screen from the Judgement games.
Spotted by Reddit user InfernusXS and verified by IGN, a tutorial card telling players how Like a Dragon Gaiden's alcohol system works is seemingly the one from Lost Judgement. Both series are made by Ryu Ga Gotoku Studio, take place in the same universe, and even feature the same locations and mechanics, but this Judgement reference in Like a Dragon Gaiden definitely appears to be a mistake and not just a reference.
This is evident by the tutorial mentioning a map that doesn't actually feature in Like a Dragon Gaiden. "Both Kamurocho and Ijincho are known for their long-established bar districts," the explanation reads, despite the game only featuring Ijincho and Sotenbori as explorable areas. These two areas instead feature in Judgement sequel Lost Judgement.
It even references the EX Gauge — the mechanic in Judgement that lets players execute special moves — that's called the Heat Gauge in the Yakuza/Like a Dragon series.
Like a Dragon Gaiden is a Yakuza spin-off and the first in the west to drop that branding altogether. Yakuza through Yakuza 6: The Song of Life (and Yakuza 0) released under the title, while the seventh game combined it with the Japanese series' name as a subtitle to create Yakuza: Like a Dragon.
RGG Studio then made the switch altogether, and what would be considered Yakuza 8 under normal naming conventions is instead called Like a Dragon: Infinite Wealth.
Kiryu returns as a dual protagonist in that game, so Gaiden serves as a side story taking place during but away from the events of Yakuza:
Read more on ign.com