Just skimmed over it, but this seems like an odd statement: "The problem of the algorithm was quickly handled. NIST, which had approved[17] Dual_EC_DRBG as a FIPS, immediately responded by recommending that the algorithm not be used and opened a public comment period on the standard."
That is... immediately after they knew nine years about the backdoor. What often gets forgotten is that in the case of Dual EC the Snowden leaks only confirmed what was already known. The warnings about the possibility of a backdoor came much, much earlier (this is from 2007: https://rump2007.cr.yp.to/15-shumow.pdf ).
This is something we may never know, but is there actually a backdooor in Dual-EC-DRBG?
It has been know long before Snowden leaks that this algorithm can be backdoored, and even without that, it was considered by researchers to have some avoidable weaknesses. The approval by the NIST is also very suspicious, why use a not-so-good algorithm, with constants that come from who knows where and that may contain a backdoor.
But while there are many claims of a backdoor, there is no actual proof. It is possible that the chosen constants are honest, or even better than "nothing up my sleeve" numbers, as it has been the case for the DES S-Box. AFAIK, we don't have the key to the hypothetical backdoor, or any mathematical proof of it existence, we also don't have evidence of the backdoor being used.
Technically, Snowden didn't say anything on that matter that we didn't already know. He may have insider knowledge, but I don't remember hearing about Dual_EC_DRBG in the original leaked document.
Anyways, I see no reason to use Dual_EC_DRBG. There are doubts, and there are better alternatives.
There is a lot of circumstancial evidence that supports the backdoor story, e.g. the extended random extension or the events around RSA Inc. and Juniper. I mean... it's a question what would qualify as prooof (a copy of "here are our secret numbers" from inside NSA maybe), but basically: There are a lot of events that definitely happened that make a lot of sense with the backdoor story and make no sense otherwise.
That is... immediately after they knew nine years about the backdoor. What often gets forgotten is that in the case of Dual EC the Snowden leaks only confirmed what was already known. The warnings about the possibility of a backdoor came much, much earlier (this is from 2007: https://rump2007.cr.yp.to/15-shumow.pdf ).