This kind of case is why I hate patents. As many other commenters pointed out, the fact that light through the skin can be used to measure biometrics is arguably "obvious" given that many people noticed it around the same time. The patent simply measures which group had the $, time, and motivation to submit a patent before any of their peers did. In this situation, the basic measurement method appears all over the place, like in cheap pulseoximeters. Sticking the same device in a wearable or other device isn't a giant leap that deserves being defended via patent law to protect an "inventor".

I'm sure patents have a place in the modern world, but I rarely see a case where they are being used as intended - more often than not, it's as I said above : a measure of who from a bunch of peers who "invented" the same thing at the same time made their submission to a patent office first with the goal of squelching competition or building revenue streams via licensing. Basically, scummy practices abusing the system. Apple certainly is not innocent in this regard - I hate it when they play this game just as much as I hate it when others do too.