In and of itself, what is actually incorrect about that statement?
I think a lot of normal people are going to smugly harp on that statement, but in and of itself it seems perfectly reasonable to believe that there's a diminishing return to safety measures for anything at some point.
The issue with this sub thing seems to be that they made some really bad choices, including apparently having glass that wasn't rated for the actual depth they were going to, choosing a gaming controller that apparently had a history of wireless issues, and other dumb issues with the design of the sub.