IP67 is resistance to about 1.42 psi of water (1 meter depth). Water falling a couple of feet, especially when being forced through a small hole in a shower head, exerts a lot more force than that, so it's going to exceed IP67 specs. Consider the water resistance an "oops resistance" - if you spill water, and it seeps across the table and gets to the screen because the phone is face down, the phone is save, but even dropping the phone screen down from a height of a few feet into a meter of water will far exceed 1.42 pounds and force water into the phone.
There aren't waterproof phones - Nextel went out of business in 2005 (and had only 1 really waterproof phone and 1 almost waterproof phone). If you're out in the rain, the Pixel is probably safe, but if you take it into the shower, or drop it into a tub with water in it, it's probably going to get water damaged. And a waterproof phone includes water damage in the warranty, the Pixel doesn't. (No phone currently on the market does.)