I honestly think the Switch will have little impact on the PS4's lifetime sales (and vice versa). Yes, there will be some effect (ie. some people who bought a PS4 before the Switch released will be satsified with owning one console, considering most people only buy 10 games per console, while some people will pick the Switch over the PS4 now and such things), but percentagewise, the impact will be small in my opinion. Of course, there's no way for me to test this hypothesis.
Anyway, I'm not surprised, because this is what the data has showed us so far. The PS4 and Switch are (launches aligned) close in the US, the Switch leads quite substantially in Japan, while the PS4 leads quite substantially in Europe. While we of course don't know how the Switch will hold up compared to the PS4 long-term, I have no doubts the Switch can easily do more than 105 million. How much more than that remains to be seen, could be a lot, could be a little, but 105 million is already a high bar.