It was a book event for that book Aoyama-san(Was the DQX technical director before becoming the current DQX producer) wrote.
First 40 people who signed up got in. Cover charge was 1000 yen(came with a non-alcohol drink). I thought it'd fill up quickly but took about 2 weeks(Filled up pretty quickly once the Host(V2,V3 director) was announced)
Famitsu has an article about it https://www.famitsu.com/news/201811/16167756.html (in JPNS) It also streamed on YouTube(the link is in the famitsu link) . Only technical questions were allowed during the event, so I asked my question during the autograph session(Main reason I went).