They said he was being a red flag but yamada atleast apologized to akane. We all know that he's new to relationships and Akane is also trying to understand that too. Yes, it was his mistake and that was really not cool of him but that doesn't necessarily make him a red flag. Also, Akane should sometimes be "selfish" too cause their relationship is two way!
I saw people from that app (TT) saying that he's a red flag and really just shows that their interpretation of the story is just not it.