Disneyland - S3-E22
Revealing mistake: The episode was filmed with real Disneyland visitors. One can constantly see them staring at the camera and/or Disneyland cast members standing with their backs to the actors, monitoring the crowd. This is especially noticeable when the family first arrives and when Mitchell and Cameron talk about Lily's leash: behind the actors, there are long white rope lines supervised by park staff to keep visitors at a distance. Several people can be seen filming the actors or taking pictures with their phones.
Answer: Mitch is upset that his dad doesn't seem to support his getting married. When they talk about Jay's friends not coming to the wedding, Jay makes it seem like Mitch wouldn't want them to come anyways. Mitch sees it as it's actually that Jay doesn't want to invite his friends to his gay son's wedding because he's embarrassed and uncomfortable about having a gay son. Essentially Mitch sees it as if he was marrying a woman, Jay would be willing so spend money on the wedding, host it at the club, and invite all his friends to it.
Bishop73