Nobody sent the Iron Wolves text messages to update them about the weather in High Pass. The skaven didn't post about fighting daemons on Twitter. The maps being posted in the thread matter.
Of course, on the flip side, the Iron Wolves already habitually raid/attack travellers on this road per Mathilde. That doesn't happen from the Iron Wolves just randomly bumping into them without looking, that happens from the tribe making it a priority to monitor the road so they become aware of potential targets in advance so they can put together whatever level of force is required (and re: "whatever level" let's bear in mind that Kurgan tribes aren't small; the theoretical upper bound could be in the tens of thousands of warriors). There's plenty of reason to think they would have been watching even without anyone tipping them off about us in particular, because there's plenty of reason to expect them to be
watching period. They don't have to be watching for us in specific to spot us if they make a habit of monitoring this road for targets anyway. Which they do, because the Skull Road isn't so clogged with caravans that you can become well-known for attacking them without even looking for them.
Also, as I alluded to before, the Plotter daemons have proven themselves to be interested in and willing to fuck with the Expedition before when they burned our supply cache. Attacking the Skaven means they'll have gotten enough sacrifices to rejuvenate at least some of their number and keep them on the mortal plane longer. And it literally only takes one to be a messenger to the local tribe of Chaos-worshipping raiders (or a handful, if they need them to spread out because they can't Tzeentch bullshit their way to just heading directly to them). That's a low-cost, potentially high-effectiveness way to fuck with an enemy through the gift of foreknowledge to Chaos's servants. Is there anything more Plotter-y than that?
tl;dr - I don't think the Iron Wolves would
need to have been warned of our approach specifically to have a quite good chance of spotting us for the reasons I said before, but I also don't think we can casually discount the possibility that they
were given advance notice of our approach.
So for once, we need to think like a grey and try not to provoke notice. Going out scouting is begging to get tangled up in something with a good chance of going loud.
...What? How does this even make sense? The Expedition already engages in regular advance scouting, because it would be crazy not to - declining to look for the enemy doesn't make them not show up. I mean. Fundamentally, the entire point of scouting as a concept is to become aware of the enemy
before things get loud. And the Expedition typically does it with detachments of fully armed-and-armored Knights on kittybirds. How on earth does a single Grey LM provoke more notice than that? And if they did spot us, how exactly would they be
more able to force, again, literally a Grey LM into an unwanted fight? The point of having
us scout is that we can more easily range out far thanks to Shadowsteed in general and in specific our having a mastery for it, and that we are the
most able to scout without attracting attention in return.
Not having us scout doesn't result in scouting not happening (thank goodness), it results in the Expedition having a shorter range within which it can hope to become aware of potential threats in advance and being less likely to become aware of potential threats without making them aware that we're aware.
And yes, the convoy is pretty much the opposite of stealthy - and while not *very* fast, is fast enough to make it so enemies would probably need advance warning to assemble sufficient force to do something to it.
IIRC, the Expedition's normal daily speed is around 40 miles. For one example of travel speeds of steppe nomads, Mongol armies were famous for being able to travel an average of 80 miles a day. So twice as fast. Also, let me emphasize, that's the Expedition's
normal daily speed. Per the QM:
This is the leg of the Expedition where the speed of the steam-wagons will reduce to a crawl and the convoy might be most vulnerable to attack
Emphasis mine.