That is absolutely untrue. Github could ignore the notice or put the content back up immediately. If they do so, they may lose the DMCA safe harbor for this complaint-- but if there is no credible infringement, that isn't of much consequence.
To do that is to assume all legal risk themselves, such that should a suit be forthcoming, it's against them, and far less likely to be thrown out, even if it's not credible. They're more likely to have to pay legal fees, and have lost legal protections.
The issue isn't their actions, it's that the process requires a 10 day wait, regardless of whether the content is infringing or not.
That is absolutely untrue. Github could ignore the notice or put the content back up immediately. If they do so, they may lose the DMCA safe harbor for this complaint-- but if there is no credible infringement, that isn't of much consequence.