You cant really say that the voltage at point "B" is 1000v, you can only say that the *initial* voltage at point B is 1000v. That's because once you use this circuit for something, that second cap will start to charge.
Even if you go to measure that voltage with a meter the cap will start to charge a little.
The question does not include anything that will close this (ideal) circuit. Knowing what voltage is there does not require connecting voltmeter. Not to say there are multimeters with with >10 GoHm input resistance with minimal impact on circuit. And you can say "initial" just about anything. Like when connecting 2 capacitors in parallel, one charged, one discharged. Initially one cap will be fully charged and another one fully discharged. Exactly the same initial result as with this not closed circuit.
It is common in theory to call the capacitor voltages *initial*.
That means before anything else happens.
10GOhm, 100GOhm, 10^99 Ohm, doesnt matter, it's still going to cause a change even though small.
Granted though this is not really a circuit yet unless we consider moisture, which will conduct very little but still some.
If one cap has 10v and the other 0v, then the initial voltage for C1 is 10 and for C2 is 0.
This open circuit is not good for anything until it is used for something, and then things change. If 1us later anything is measured, the change starts. If 1ms later, then the change starts then. If 10^99 years later something is measured, then the change starts then. So it's common to call the cap voltage *initial*.