All it's saying is that the two types are related, but that no implicit conversion exists so it won't let you "just assign" the value - you can explicitly cast it because an explicit conversion does exist, but you have to make the compiler understand that that is what you wanted to do.
Because you declared
it gets it's type by context:
var Query = DB1.view_people_history.Where(u=> u.PeopleID != 0);
And that makes it an
Your subsequent Linq code returns a related class:
but that isn't exactly the same type so the system wants to make sure that is what you intended.