That's just nitpicking. They blocked the enabling of a setting which allows Linux to see the hard disk. They went out of their way to make a firmware change that has the effect that you cannot run Linux - unless you flash your BIOS or you write a driver. In my book, they effectively blocked the installation of Linux.
Now, there are two options. 1) to support this hardware correctly, you'd need to make complex changes to the driver. In this case, I cannot see how it is the Linux' developers' "fault" that this doesn't work. It would be great to have a driver, but it depends on information that Lenovo doesn't give out. Or 2), it is trivial to make a driver, e.g. you just have to look for a certain ID. In this case, I would also blame Lenovo or MS, for there would be no reason to bock AHCI to "ensure a good customer experience" etc.
Whether this situation has come from malice or not, I don't care very much. Anyway, I think it is up to Lenovo to provide a solution (a BIOS update, a Linux driver, or information neccessary to write a driver).
Now, is it a conspiracy or not? I'd say the most likely option is carelessness. Maybe this happenend: "Shall we set this to AHCI or RAID? Currently it is set to RAID and works fine." - "Do we need AHCI?" - "Nah, Windows 10 runs fine, maybe for some older OSes" - "We don't care about those, just leave it on RAID. And while you're at it, comment out the AHCI option."
Did MS give any instructions to Lenovo to block Linux installs? Maybe not specifically, but we have to remember this is a "Signature" edition laptop. (There was the accusation that this only effects the signature edition and not other editions, which would be particularly damning btw..) I wouldn't be surprized if there was an agreement like. "The partner (Lenovo) shall install any crapware on Signature edition laptops. They shall not not preinstall other OSes. And they shall not offer support on installing other OSes." -- Which would be entirely reasonable for a special "Windows Signature" edition laptop.