The author didn't link to the actual PR so I can't see the full context, but I don't see the point in setting up a bot to make contributors agree to copyright terms if the maintainers just ignore it when someone does a PR and then doesn't engage with the bot. It seems like a waste of time for all parties.
The extra useful context I spotted at the top of the blog post was that the project falls under the auspices of the .NET Foundation [0]. The .NET Foundation like several of the other FLOSS foundations/conservatories/archive/consortiums requires a CLA as a CYA in extra part because of the legality concerns that for a project in the Foundation they want to make sure that you understand you are contributing not just to that specific project, but in general as a collective effort towards the Foundation.
This may be an interesting discussion for the author to have more directly with Foundation leadership and legal on what the expectations are.
There's also yes, the larger discussion on if Foundations such as this are possibly too conservative in their FLOSS bureaucracy/red-tape for smaller contributions to smaller projects. Under the good for the goose/gander assumption it's easy to add the same bots to every project and assume that's good enough, but does it stifle innovation or bug fixes on projects with fewer eyes?
