They were probably bringing their overly sensitive dislike of a cultural point of view into it when none was intended. They probably should have considered that HN is a broad community. As such they would know that HN has non native speakers. They would have realized that their interpretation was likely off the mark for this or another reason. They should have more charitably interpreted it as a typo and they should also have realized that their viewpoint on the singular use of “they” was inaccurate since they have probably heard such usage their entire lives but only now, in recent years, are they are just beginning to listen for it. They probably are not aware that this usage extends back long before everyone currently alive, but I guess this is new information for them. But now they know so hopefully we won’t hear such comments from them again.