I'm not really surprised, I'd actually assume that sexy John Oliver and the other protests created a lot of additional traffic. People post like crazy and a lot of people want to see that, especially since it got some coverage on news sites. Add to that the big majority of people who do not care (remember that 80% of traffic was still reached) plus some who may have been sympathetic enough to join the two day protest but don't care enough to continue to stay away. It's really not surprising that we're back to normal numbers.
Thankfully this isn't the only impact people currently still make, so this isn't over. The real question now will be how else it might change Reddit.