It is a giant plot hole. But there are so many more. The intro does show the mindflayers picking people at random as hosts yet the random selection leads to a group of survivors as follows:
A vampire spawn
A wizard with explosive shadow magic inside of him
A warlock in pact with a Devil
A shar cleric on a secret mission to steal what likely is an infernal contract
A githyanki
They were capturing people in faerun, not in the wheel
