No, it’s actually far worse than that. This is like if you bought prestressed concrete rated for 100kg and you loaded it with 50kg. This is less than the limit, so it’s good right? Nope, the way it works is that you have to give it exactly 100kg of load or else it’s weak to tension and your building falls over in the wind. The problem here is that not that they needed 521 bits of entropy and 512 was too little but that 521 bits of entropy of which 512 are legit and the top 9 bits are all zeroes breaks the algorithm completely and makes it not secure at all. In fact I think copying 9 bits from the other 512, while not great, would have probably made this basically not a problem. I am not a cryptographer though, so don’t quote me on that ;)