To be honest it’s not lying, the advertised kernel is part of the history, it’s ignorance. It’s just that it got so many unintentional modifications as the result of merge conflict resolutions that it’s very far from the claimed kernel, and such changes are extremely hard to spot.
The best way to see these changes is by running git diff between the claimed kernel version and the whole kernel, and seeing changes that are clearly not related to the BSP. But many of them are less clear because you have large areas where maybe one line came from the intended BSP changes and the rest is just failure to merge new kernel changes in the vicinity that appear as context changes.
Now depending on what you intend to do with that device it may or may not be a problem for you. For the vast majority of users it will only be a problem when they want to refresh the kernel, but by then (6 months / 1 year), most of the device will be supported in mainline (again, also depending on what you’ll do with it).