I'd be curious to know what "WiFi" means here exactly. If it means "my flight plan is stored on the internet and I didn't save a local copy" then yeah, I think that's insane. But if it's a local WiFi network it doesn't seem so weird to me. You should, in the course of day to day operation, be able to expect a WiFi router will work.
Of course, it'll fail at some point, but it's not like they were cut off from the world, they could have radioed for the information if the copilot didn't have it, or something.
Enterprise WiFi networks work better but my experience has still been far from what I'd call reliable.
I'd like to say an airplane might work better as a controlled environment than an office building, but probably not if you have 300 passengers in the back, half of whom have forgotten their MiFi devices running in their carryon.
Of course, it'll fail at some point, but it's not like they were cut off from the world, they could have radioed for the information if the copilot didn't have it, or something.