"""Note that this chart does not show the spectral properties of the cones themselves (but they look similar). It represents the CIE 1931 colour space, which, simply put, corresponds to the signals after they have been processed by the brain."""
"""The reason why purple and violet look similar to us is because they stimulate our cones in a similar way, but most other animals don’t share the same types of cones and “post-processing”. This means that to other animals, purple and violet may look completely different!"""
Emphasis theirs. This is the part I'm calling out. Stimulation of the cones is not relevant!
(Of course the cones are relevant but the difference is very much larger and of a different nature than they make it out to be. Most mammals have only two color cones.)