I don't know what tptacek based his words on github takedown requests on; I'm basing mine specifically on the comment by 'R' to the blog post. You make a point elsewhere that the post's author's repository is live on github, but that's not the original one, which was removed by its author. The way I understood the comment by 'R' was that they forked the original repo, and the fork was silently deleted, perhaps due to a request by Dropbox (DMCA or otherwise) that followed up to the original author's voluntary deletion.
To be sure, it could be a misunderstanding, a technical glitch, or an attempt at trolling. The Dropbox folks aren't getting my benefit of the doubt on this, though. Their actions, even the ones that aren't disputed, have been unbecoming. Banning the code distribution on Dropbox was a particularly ham-fisted move. It does nothing to curb its spread, because Dropbox is not a web-forum with easy discovery. If I put this file on my public Dropbox folder, the only way others will know to look there is when I advertise this elsewhere, not on Dropbox; but if I'm motivated enough to do that, surely it's no trouble for me to just host it elsewhere.
So the ban only hurts their image more. What if I write a text file with the description of their client-server protocol and put that on Dropbox, are they going to ban that file, too? When you willingly put yourself on a slippery slope, be ready to find yourself sliding.