Dipper IS trans (ftm) and his parents are sota supportive, but not really. (Mabel is VERY supportive of Dipper) So when the twins parents called Grunkle Stan, they told him to push more girly things on Dipper and how Dipper thinks that "she" is a boy, and how that needs to get out of "her" head.
Grunkle Stan being Grunkle Stan and not doing everything he's told to. He thought Dipper was a boy so that's part of the reason he pushed him to do all those chores. More "boy" chores to get him that build or something like that. Or to make him feel like an actual boy. And would help him get those hormone pills.
Idk, just a headcanon, not saying it's canon just a thought. Have a great day/night.