"Nowhere do I see mention of these arduinos being special, radiation-hardened versions. Nowhere, is there mention about extended temperature range, vibration, etc. These are all important if the mission is expected to succeed."
Most small satellites do not use radiation-hardened components. Rad-hard chips provide 1/10 the power at 10 times the price, and thet aren't available when you need them. Generally, they're made to order with long lead times.
It's generally easier to add a watchdog circuit to reboot the computer when it crashes due to a radiation event. Even the laptops aboard ISS are not rad-hard.
In higher orbits and interplanetary space, radiation levels are higher and rad hardening becomes a bigger concern. Even there, techniques like spot shielding can reduce the number of components that need to be hardened.
You might want to consider the possibility that maybe, perhaps, people who have built and operated satellites professionally for organizations such as NASA are not idiots and have some idea what they are doing.