I'm not familiar with the propeller reversing system on the LET 410. However, in general, it is correct that "reverse" and "beta" are two different things. Both will result in reverse blade angle upon pilot command, but how it got there is different.
For my experience beta systems have a guard or gate to prevent inadvertent selection out of "forward". Some of those systems can be overridden by the pilot in flight, others not. Barring mechanical failure, beta (flat pitch, or reverse blade angle) selection will be the result of the pilot moving the engine power level aft. I would credit a pilot with not selecting only the right engine into reverse in flight.
There have been numerous accidents resulting from eager pilots selecting lots of beta upon touchdown, to achieve a short landing. It has happened that one propeller did not enter the beta blade angle, and the asymmetric thrust resulted in a loss of control on the ground. I speculate that some turbine parachuting aircraft may be operated in beta range coming down following the jump run.