Something similar happened recently with A320 when it didn't want to land on an airfield during emergency unless it was flown in a special mode. But F-35 doesn't have that?
Think of it as various stability control modes in a modern car. Likely the aircraft needed to be put in the least restrictive flight law mode as a workaround.
An Airbus can operate in three modes. With Normal Law, the airplane will refuse to do anything which will stop it from flying. This means the pilot cannot stall the airplane, for example: the computer will automatically correct for it.
With Alternate Law the pilot loses most protections, but the plane will still try to protect against self-destruction. The plane no longer protects against being stalled, but it won't let you rip the wings off.
With Direct Law all bets are off. Controls now map one-to-one to control surfaces, the plane will make no attempt to correct you. All kinds of automatic trimming are lost, you are now essentially flying a Cessna again. The upside is that it no longer relies on potentially broken sensors either: raising the gear while on the ground is usually a really stupid idea - until the "is the plane on the ground" sensors break.
So no, a "Boot in safe mode" isn't as strange as it might sound at first glance. It significantly improves safety during day-to-day operations, while still providing a fallback mechanism during emergencies.
Notably, most drones have similar levels of control. Everything has to go through the IMU of course (nobody is manually going to be managing 4 separate motor controllers at once), but depending on the modes, the type of control is wildly different.
‘Consumer’/‘idiot’ mode - you tell it which direction to go, and how high/low you want it, and it’ll do that safely. Usually with some sort of object detection/avoidance, auto GPS input, so you won’t accidentally wander into something or hit something. Goal is stable, level flight.
‘Sport’ mode - go fast, usually disables all but the most simple collision avoidance. Sometimes even that. Still provides stable, level flight, but you can easily crash it. Usually goes 2-3x faster than ‘idiot’ mode.
‘Attitude’ or ‘acrobatic’ mode - you’re directly commanding the target 3D pitch/yaw, and aggregate power output. No provision is given to automatically maintaining level flight (won’t auto level), generally no regard is given to airframe integrity, collision avoidance, or engine life, and boy is it fun.
It’s really common to crash in this mode, because people are also doing flips, acrobatic maneuvers, running courses, etc.
Drones in even ‘sport’ mode can’t do flips because it’s fundamentally at odds with auto maintaining level flight, etc.
Changing the law of the aircraft is something you REALLY do not want to do. It's a "The Airplane broke real bad, do that pilot thing!" situation. Especially on a fighter jet with relaxed stability.
https://www.airliners.net/forum/viewtopic.php?t=748133
Some fighters have an "EFCS" switch which will switch laws. This can be used during "I'm going to fly into the ground" or "I'm losing this dogfight" situations. Typically this means you are going to be scrapping the airframe soon one way or another.
The above post is focused on a Sukhoi jet, with some comparison to Airbus' design, but they also cover Airbus in another post: https://admiralcloudberg.medium.com/the-long-way-down-the-cr...