I don’t think he forgot about that scene, I just think he kinda sorta wrote himself into a corner. Padme would have to die somewhere in the prequel trilogy regardless. It is bad story telling to have a principle character survive a chapter, but to never be shown again in the rest of the story.
But her disappearance was already explained in the 6th film, so there was NO need to kill her off. That’s not bad storytelling. What is bad storytelling is to contradict so many things in a saga where the second part was filmed prior to the first part, where the story was already set, but you still end up screwing things up that were mentioned in the original films. For eg:
OT- Owen was afraid that Luke would follow Obi-wan on some damn fool idealistic crusade, like his father did
PT - Owen never even met Obi_wan while anakin was alive and Anakin didn’t follow him on a crusade either as, by the time owen was even in the picture, Anakin was already a jedi and it was Qui-Gon that he followed originallyThe reference is to when Anakin went off to fight in the Clone Wars. Following the death of his mother and the funeral, Anakin and Padme are summoned back to their ship when a message from Obi-wan has been detected. Anakin leaves shortly thereafter and three years later, the Jedi are blamed for trying to overthrow the Republic and Anakin is among the casualties in the Jedi Purge. Owen felt that Anakin shouldn’t have left to fight in a war that he was going to lose. This anger is directed towards Obi-wan, after bringing him Luke to raise. This is why he doesn’t want Obi-wan around him and doesn’t want Luke to know about his Jedi heritage. And why he doesn’t want Luke to go to the academy. He’s afraid that he will lose his life like Anakin did.
According to the PT, Owen never even knew Anakin. A step-brother he met very briefly. Why the hell would he have even cared what the hell happened to him? And why the hell woudl he be angry at Obi_wan fro bringing him Luke to raise? That would just make Owen an asshole that never wanted Luke in the first place, so why the hell would he be so protective? He wouldn’t. All of that is just trying to make stuff up to try and forgive bad writing. It’s bad writing plain and simple when fans, and spin off books that come later, have to try and make sh*t up to try and fix massive problems that shouldn’t have even been there in the first place when the ground work and situations were there from the start. A good writer would know how to do that.
Owen knew enough from the five years Shmi lived with him. And the fact that Anakin failed in his endeavors, which got him killed and force Owen to take care of his kid, these are reasons why he feels this way later on. If Anakin hadn’t gotten involved, he’d still be alive and taking care of his own kid. Rather than dying in a senseless and futile conflict.