Yes it's a single battery pack burning and you need to keep it cool with larges amount of water for a long period to let it cool off so it doesn't restart.
A second pack or a separate cell inside the same pack? These things are highly modular and even within a large pack there's multiple smaller packs that are also fire insulated against each other.
Seems pretty clear from this photo[0] it spread to a second pack that was in close proximity. A quote from the media release is "They found a 13-tonne lithium battery inside a shipping container was fully involved" which would exclude the possibility that it was a single pack within the container. This is also shown in the photos.
