James, thank you for your interest in Japanese simutrans community.
Actually, the videos you noticed were our 4th simutrans conference. The
first japan simutrans conference was held in Yokohama in May 2017.
The second was in September in Sapporo Hokkaido, the third was in Yokohama again in December 2017, and the forth was in Kyoto in December 2018. The japan simutrans conference is an event in which players present their simutrans knowledge. In the last conference, approximately 25 people attended and 12 people did the presentation.
Unfortunately, the videos of these conferences are not well datanyzed. Although we call this event as "conference", it is not a solemn event as academic symposiums, but a casual gathering event of the Japanese simutrans players

Does anyone here know anything more about this? I believe that Phystam of this forum might have been involved in the Pak.256-Ex presentation: he is certainly mentioned, although it is not entirely clear from the video (at least, to somebody who does not understand Japanese) whether he was actually speaking at the conference. There was also a presentation on the OTRP, suggesting that THLeaderH might have been involved, too.
This is correct. The man who spoke about pak256-Ex in the video is phystam, and the man who spoke about OTRP is me, THLeaderH.
and a brief summary in English of what was discussed in them would be wonderful.
OK, I made one or two lines brief summaries for each presentations.
01: Opening Session
02: "Urban development theory and simutrans" This video describes how to build a beautiful city using knowledge of urban development theory.
03: "Jiyu-cho - the making of a simutrans guide book" This video tells us an inside story of the presenter's book, which is a guide book of simutrans for new players and intermediate players.
04: "Action Report 2018 of making simutrans BGM" The presenter of this video is one of the contributors of the recently posted simutrans musics. This video is a talking about making simutrans musics.
05: "Making a stylish thumbnail image of simutrans add-on" The presenter is a vehicle add-on author. This video describe how to make a stylish thumbnail image of simutrans vehicle add-on.
06: "Beautiful World for Simutrans" This video describes how to make a beautiful urban and rural scenes in simutrans through a demo.
07: "Reproduction of real world using Mercator projection"
08: "The development of pak256-ex on simutrans-extended" The presenter of this video is Phystam. This video describes the concept, constraints, making methods, project management, and some parts of pak256-ex.
09: "Various play styles on Net-Simutrans" The presenter of this video is a server owner of simutrans network game. This video shows some interesting and funny scenes in his server.
10: "The world of network games" This video describes how Japanese plays network games and how the network game feature affected Japanese simutrans community.
11: "Congestion theory in simutrans" This video describes congestions of road vehicles in simutrans theoretically.
12: "Application of road transportation of real world to simutrans world" This video describes the characteristics of road transportation in simutrans and discusses how you can use buses effectively. This video clearly explains the role that road vehicles should play in simutrans.
13: "Report of Simutrans Game Engine 2018" The presenter of this video is me, THLeaderH. This video describes new features developed in 2018 for simutrans-standard nightly and OTRP.