I think it would be prudent not to have other apps running when using such a device for navigation. However, learning how to switch between apps would have helped.
Well he had inavx on his iPad and iPhone but only had the waypoint on his iPad. He didn't know how to operate the iPad and he failed to stop and find out where he was when the app on the iPad froze. I assume he had the waypoint LL written down somewhere? Perhaps on a chart? Or was it in the pilot book? Or even on a scrap of paper with the rest of his passage plan and pilotage?
He's blind so good on him for sailing transpac but he's also a bit dim so I'm glad he didn't hurt anyone.
You should close all apps if only to preserve battery life. Many people don't seem to realise that just pressing the home button on the phone to get to the main screen doesn't close apps.