In Warlords of Draenor, Garrosh arrives a couple of days before the orcs are supposed to drink the demon blood. Just in time to warn them and stop them from doing so. Grom Hellscream then becomes warchief of the Iron Horde.
When compared to Rise of the Horde, that makes no sense at all. In the novel, Blackhand had been elected warchief of the Horde long before they ever drank the demon blood. They had slaughtered hundreds of draenei long before drinking the blood. Hell, even their skin was turning green already. The warlocks already existed, and the Shadow Council had been in power for as long as Blackhand had been warchief. They only drank the demon blood when only Shattrath was left, the draenei's last stronghold.
In WoD, things are completely different. Blackhand isn't warchief yet, the clans are divided, there's no apparent Shadow Council in place, and most jarring of all, the draenei are still numerous and prospering.
It seems like there are huge differences between the main timeline and the alternate timeline, even before Garrosh intervened. In fact, Mannoroth is not even present when the orcs drink the demon blood in the novel, yet he's standing right there in the WoD opening cinematic.
Weird.
Also, I have one more question about the main universe itself, something that doesn't make much sense. Right after invading Azeroth, it says Gul'dan banished the Frostwolves to Alterac Mountains. Now how the hell did they get there? The orcs came through the portal in the Swamp of Sorrows (then the Black Morass), which is at the very south of the Eastern Kingdoms, and the Alterac Mountains is in the far north. The Frostwolves would have had to travel through human and dwarven lands to get to Alterac, even through Lordaeron. How did nobody notice that?