While it's possible this could be a simple slip-up on Sheldon's part, it seems unlikely given how detail-orientated he is. In "The Big Bang Theory" Season 1, Episode 11, "The Pancake Batter Anomaly," he tells Penny about his mom Mary (Zoe Perry) accompanying him to Germany, "My mom had to fly back to Texas to help my dad because the house slipped off cinderblocks again," Sheldon continued detailing, "It was tornado season, and it was an aluminum house." This lines up with what we can expect in the following episode of "Young Sheldon," as we even overhear high wind warnings during Mandy's (Emily Osment) viewing of the evening news.
Since the terrifying tornado detail remained the same, it's possible that Sheldon's childhood trauma led to an instance of misremembering when it comes to the events from his childhood. After this life-changing adventure, Sheldon endures a tragic loss when his father George (Lance Barber) unexpectedly dies, which likely won't happen in Season 6. He then moves hundreds of miles away from his family to start graduate school in California, which is enough sudden change to muddle anyone's memories.
In between these milestones, Sheldon will also have an awkward and emotional scarring moment with his father that gives him his unusual knocking habit. This could also jumble his memory and lead to the mixup in his later retelling with Penny. In reality, though, the writers most likely want to move along the narrative to these key moments without having to do a time jump.
