But the tires look less fat, like a 3.0, maybe. 650b x 3.0?
If it is a 622ISO based tire, Surly will have pulled a coup of (pardon the pun) massive proportions. It has been well documented that 29"er tires could not be made larger than 2.4" wide-2.5" wide due to the physical limitations of the tire molding machines used in Asia.
So, unless Surly got someone to produce a super-expensive mold machine, and then use it to make this supposed 622ISO bead tire, it isn't (probably) a 700c based tire. (Don't say 29"er. It would be a bigger diameter than that if it were a 700c/622ISO tire @ 3" width)
Of course, there is always that "if" hanging out there until we actually see it.
And it could very well just be a wider rim with a 2.4"er on it as well.

Those have been done before, maybe Surly is doing that idea one better.