FP5 owner here. IIRC, this is a guarantee for security updates at least, yes. There was some promise on how many major android updates they guarantee I think, but I forgot the details. I also wonder if and how far the promised minimum will be exceeded.

That said, I am just glad Fairphones are usually relatively well covered by open source versions of android and other operating systems. Even if I may need another phone for banking apps and all that annoying stuff in 2030 or so, I can at least safely re-use it for other purposes. My "old" Android is now nothing more than an offline mp3 player, which is kinda sad.