Well, the dude said "at 55M," which seems like an awfully round number, but if we take it at face value, EA would have Bone "at 19M." (19.1M, I guess.)
Someone at MS gave Mary Jo Foley "around 18M" as a number for the Bone, but it's not super clear what they were actually describing. In theory, it was just Bones that had used W10 in the four weeks preceding, but it could've easily been a count of the total number of Bones.
Could Bone be at 17.9M, and EA estimated 18.3M or even 18.7M then called that 55M total? That seems entirely possible. Could MJ's leak have really been describing activations, and the actual sell through is closer to 19M? Perhaps, but I still find it unlikely an MS rep would say "around 18" when they could've easily said, "nearly 19," or even, "around 19," knowing we'd never have any more than vague stuff like this to check it against.
So, 18M-19M seems pretty reasonable. I'd guess towards the lower end, but I can see those inclined to be generous favoring the upper end. Seems unlikely to be much outside that range though.