According to the article, the audio feed was a backup, and a third party supplier misused it. It definitely wasn't someone "realizing" that there was a public audio feed with a lower delay.
>the Bank confirmed that a third party supplier “misused” an audio feed of certain of the Bank press conferences since earlier this year. The audio was installed to serve as a back-up in case the video failed.
That analogy only works if the BOE makes both streams available on a public basis. If the company is contracted only to provide a backup stream in case the primary failed, it stands to reason that they do not have the rights to stream/broadcast during normal circumstances. From a legal standpoint, it would be similar to eavesdropping on the live press conference using a bug.
Both parties have blame and one of them is trying to throw the other under the bus.
They may even have thought that a few seconds could still be called synchronous, unaware of the advantage this presented in this particular case.
The supplier was selling access to it without the right to do so, and knowing full well what they were selling.