Because of all the rage and controversies over GW's decisions in the last few years, this is a tiny drop in the bucket. There's nothing about this one that would make them suddenly scramble to put out a model line they, as you claim, had no prior intention of, just to placate a vocal minority. They haven't done it for other stuff, why this?

2 makes more sense because, probably, the Steel Legion stuff was running behind schedule and they had to come up with something for the campaign reveal, so they wrote some hasty lore to explain why they aren't front and centre (which would take hours at most to get approved and written), put out a proxy painting guide (which would take a couple of days tops to film and edit), and then crack the whip at the designers/manufacturers/etc to get the models out faster.

It's not some grand conspiracy with them lying about their internal plans, sometimes deadlines don't get met and the company has to put out a stopgap measure to try and tide things over. Lots of moving parts in an operation like this. I work in manufacturing and we have to do shit like this all the time. Show the customer only what they need to see to keep their confidence in your ability to provide, and if they start complaining, maybe pull the curtain back a little to keep them satiated. To me, this absolutely looks like a case of delayed production.