Speaking of opinions, I presume from an expert where as am not:
"However, there’s a number of implications of this being bandied about which are wrong."
And he is correct?

The reason producers were increasing production was due to demand, mainly from China, and China slowing down has resulted in the over supply.
Prices were high because there was a demand, now that demand is much reduced so prices have fallen. However producers can not increse production at a drop of a hat. It takes time to increse supply. Just when that supply was nearing demand the demand reduced = glut.

What the producers may be guilty of is in not being able to foresee when the boom would slow down and reverse. China is secretive enough to make such sight fairly difficult.

Just offering a contrarian opinion, and we do not need to agree even with experts.