The ECB printing money is a factor in stabilizing rates but it in itself does not create conditions where governments are able to borrow for 30 years at negative rates. For example, if the deposit rate was at 3.00% instead of -0.40%, governments would not be able to issue at negative yields; QE or no QE. Additionally, the ECB stopped net QE purchases at the beginning of the year and negative rates are still a thing.
