@horrifichymns My guess is that since Flowey was the first ever Undertale player (as in, he was the first to be able to save, load and reset in the underground), his save file was made since the Undertale Demo.
And he replaced our save file with his.
1/2
@horrifichymns meant to mess with players who played the DEMO of the game before it came out, this was how it looked originally
in-universe this must be the game freaking out from Flowey glitching the game by taking over the SAVE menu, and so it shows a deprecated version of the intro cutscene
@horrifichymns I always interpreted it as something that's meant to catch the players attention and make them debate whether or not they were just misremembering the opening, all for the purposes of making them linger on the intro for long enough so that the spook gets them