I'm not that surprised by the Dragon run jumps. You had 2x speed set drops, so if only that, it was worth running a little more than usual.
What i think happened, and this is just my 2 cents, i could be very wrong, but.... There's that game that just came out which broke its company records in sales for first 10 days.. You know that game which is the 4th, but not quite, because the 3rd is 10 years old, and the "official" 4th comes out later.
Anyways, reviews from hard-core gamers are pretty bad, but nevertheless, it could have had an impact on our player base who are temporarily occupied with their new toy, but who will soon get bored and then come back :P
I didn't think about the 2x speed rewards, so you are right in that this could be a reason behind the growth. It is odd that people would run Dragon 25 specifically just for speed sets though, because from an energy and time point of view, generally people stick with Dragon 20, 21 or 22. The chances of rewards are similar.
That said, there was another spike in Dragon runs again in the last 24 hours, with it gaining another 1 million, but the 2x speed event would have been over completely by now. The event ran from 23rd Jul to 26th July UTC, and while yesterday might have been on the border (it was 27th UTC when I got the figures), today is currently 28th UTC.
The other theory is that the reported figures online are 24 hours out of date. This would explain why some of the spikes with Spider took place after fragment of CvC events had finished.
Currently there is a 2x Retaliation set for Ice Golem. Wonder if we will start to see that spike up soon. I doubt though