1st and foremost the CBC does not use the model IRC for Guard height, its the only state in the USA that requires all guards on open sided floors or balconies to be 42 inches high period. The only exception is on stair flights within a dwelling unit.
So, ICE not understanding what the other 49 states do allow, I get. ;>)
As to the R-2 and separate means of egress, it is simple.
There are parts of the country were they build stacked 2 story condos. Hence the first 2 floors, less than 3 stories, all have their own entrance to the public way and is not shared, then on top of that, there continues to be condos, built lets say going up another 10 stories.
Hence the 2 story street level units with the separate entrance, not sharing M.O.E. are allowed to take advantage of the IRC guard height of 36".
The unit is no different than a townhouse 3 stories or less, for the owners or tenants, except for those above 3 stories.