"Solved" means having a solution to a problem. In context, we're talking bout whether or not neural networks can detect truth better than "decades of work by experts to reach consensus." So, in this case, solving would be detecting truth better than the status quo, not detecting truth 100% of the time. In the example of Go, the problem was "playing Go better than the best humans." So in that sense, the problem was solved. Adding your own, unfavorable definition of "solved" to the discussion is unwarranted.