It's generally boring misremembering then constructing a narrative around that, then people come up with wild theories to explain simple misremembering and the brain (or the individual) making things up.
It's like with the 'Mandela effect' where people claimed they specifically remembered Nelson Mandela dying years before he did, when what they remembered was the extensive coverage of his release from prison. Then that was extended to many other accounts of misremembering which where then attributed to time slips or glitches in the matrix or whatever nonsense.
My favourite is in the UK, the idea that Walkers crisps swapped the colours for cheese and onion and salt and vinegar.
Which never happened. Walkers even put out a statement saying their C and O had always been blue, and S and V always green. Which led to lots of bizarre conspiracy theories about why Walkers were lying. I mean, why would they?
There have been several threads about it on MN and hundreds elsewhere with people railing about how they very specifically remember when Walkers swapped the colours.
The problem being that not only did it never happen, all the very specific memories people had of it happening span decades. Some people relate really detailed 'memories' of it happening in the 1970s, 1980s, 1990s and early 2000s.
So even if Walkers were for some bizarre reason, lying, it still couldn't possibly correlate with all those people's 'memories' and narratives.
What actually happened was Golden Wonder always had blue packets for S and V and Green for C and O. Walkers the opposite. Golden Wonder was the most popular brand for years so people identified with the colour scheme. You picked up a packet of blue crisps knowing it was S and V.
When Walkers started taking over as brand leader, people started picking up blue crisps not paying attention to the brand and got Walkers C and O.
Which led to the idea that all crisp makers had had blue meaning S and V so Walkers had swapped the colours.
The rest of all the conspiracy theories were all the people 'specifically remembering' when Walkers changed their colour scheme because one day they picked up a blue packet of crisps and were shocked to find it wasn't the flavour they intended to buy.
And the rest of it is just about how susceptible people are to implanted/false ideas and memories.
Like all the people who think they saw the first plane hit the twin towers on 9/11 and think they have specific memories of how shocking and traumatic it was, when the only footage of the 1st plane hitting the twin towers was filmed by 2 French brothers making a documentary about NY firefighters who just happened to film it and it wasn't on TV the day of 9/11 and came out later.
False memories. Susceptibility to implanted memories and then curating a narrative around that. It doesn't mean people are lying, just misremembering and then constructing a story around it.