This is correct - for once FP is wrong here. Logically, you'd think that the oldest surviving son/child of the monarch would be the next in line, but this isn't the case. If Charles were to die tomorrow, William would be the heir to the throne, and his son, George, would be second in line. Harry would be third in line, and Andrew fourth. If Charles and William were to die tomorrow, George would be the heir to the throne, over both Andrew and Harry. For Andrew to become the heir to the throne, Charles and his entire line, i.e. William, Harry, and George, would all have to die before him.
This seems a bit illogical, as one imagines "monarchy" to sit in the current monarch and then pass to whoever is the oldest son/child of that monarch upon their own death, but I assume the reasoning behind it is that it preserves stability. I.e. as things currently stand we can be pretty confident that William will become king at some point, unless he dies first; and it makes no difference whether Charles predeceases his mother or not. If Andrew were to become next in line upon Charles' death there would be greater uncertainty about where things are going. Not, of course, that it makes any practical difference to anyone other than the people directly involved.