I don’t think that’s true. The official argument is that human operation wouldn’t reach the required reliability level (https://www.cs.vu.nl/~x/sil/sil.html: “The failure rate demands for this system were required to be 1:10000 for not closing when this was actually necessary, and 1:100000 for not opening the barrier when requested. This asymmetry is caused by the fact that if the sea surge barrier does not reopen, the river discharge can lead to flooding from the inside.”)
I think nobody knows for sure whether the conclusion that software alone would be more reliable than humans alone was correct (my money would be on “it wasn’t”). That’s hard to verify for such a system that “cannot be tested under the conditions for which it was designed” (https://www.researchgate.net/publication/220592956_Human_fac...).
You can’t do that statistically, either, as in real-world use it would take millennia to collect the necessary data, and that’s way longer than the design life of this structure.
Which makes it all the more unique that it closed, because there's a lot of water coming down the Rhine and Waal right now.
Rijkswaterstaat (who manages all of this) prepared for this by making more space for the river water to flow and flood in other directions.