Philip K Dick's speech is about a simulation that gets altered along the way, leaving the actors in it with some residual memories and/or deja-vu. Which is what he tells of having experienced.
Bostrom's theory - which Elon Musk is talking about in the first video - is different.
Bostrom says that: imagine first that humans don't wipe each other out or otherwise go extinct (nearby supernova, anyone) and keep developing technologically.
At some point in the future, humans would have enough computing power - say even something planet-sized - to simulate millions (billions) of human beings, each with thoughts, feelings, interactions.
So, if our descendants have that computing power, then they might be interested in running ancestor simulations.
If that is the case, then there could be millions (or more) of these simulations. if that is the case, then it is exceedingly likely that we are living in one of the simulations and not in "real" life.
Of course, there are a lot of ifs. Can consciousness be simulated? Would our descendants want to or even bother running ancestor simulations - what for? There are moral questions about running such simulations - each simulation generates tremendous suffering, starvation, murder, etc that is indistinguishable from reality for the participants.
I think these are interesting academic exercises, but unless we figure out how to "leave the Matrix", if there even is one, then we are stuck here (ie either in real life or in a simulation, can't tell), in which case, might as well make the best of it and be the best version of yourself.