paging icebreaker for immediate application of the MP-RDF. These truths cannot be left unFUDed in public!
That yes/no image is incorrect.
If core is the longest chain and someone is stupid enough to mine an XT block that core doesn't allow, then all XT nodes will follow the XT block fork.
Thus if core continues to be the longest chain (which it will) then XT clients will not follow the longest chain possibly until later.