First of all, it isn't really known yet which object it is, at least to the general public. Space Track (JSpOC) no doubt knows which object it is, but it would require them confirming it to the public to get the positive identification. In order for them to release this information to the public, it requires a high level expert to confirm the information, who normally doesn't work on weekends or nights. I expect the confirmation will be done today.
That being said, there are a few bits of information we can use. Of the 6 objects that are being tracked, 3 of them are in a lower orbit then the others. We know from publicly released information that Humanity Star is supposed to be in the lowest orbit. One of these objects is positively identified, meaning that it must be one of the two remaining objects, D or F.
Given that Humanity Star was a secret payload, not announced to the general public until after launch, I suspect that it was given the last designated payload slot. In addition, "F" is the lowest object at the moment, and is given a "Large" Radar Cross Section (RCS) size by JSpOC, as is object "D". It seems like Small, Medium, and Large are the most commonly given values for the RCS size.
Lastly, the common convention of JSpOC is to give all payloads the first levels, followed by any booster stages, and finally any debris objects. It is worth noting that there are 4 "Payloads" that were launched, in addition to 2 "Booster" objects.
That being said, I'm confident that JSpOC things that "D" is Humanity Star", and "F" is the spent second stage booster. "E" would be the spent third stage booster, and "B" and "C" should be the two Lemur satellites. I wouldn't make anything official until JSpOC releases the designations, but I believe 43166 is the proper designation for Humanity's Star.
So, I was wrong, the real one is the "F", 2018-010F 43168. I suspect that the two looked alike, and they initially guessed wrong between Humanity Star and the booster stage.