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.
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.
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.
The supplier was selling access to it without the right to do so, and knowing full well what they were selling.