It does seem a bit weird for the chapter to be tagged with both yuri and nakadashi. I wouldn't have thought that it would qualify as yuri when there's a guy taking part, but I guess that it got tagged with yuri, because the girls are doing each other as part of the threesome rather than just doing it with the guy.
it seemed like the girls were more into having sex with each other, even though the guy was there too. especially by the end. not fully yuri, but just yuri enough, imo.