If it's not officially supported, it probably means it's just one or two people that open sourced it, and it would fall on them to keep it in sync with any internal work.
Officially supported means it's actually owned by some team. They'll dedicate resources to it, meaning it will be accounted for on any project planning or resource management the management needs to do.
"Official" is mostly about who they consider the customers of the product when making a decision.
If the project is officially open-sourced, that will be taken into consideration when project priorities, re-orgs, and direction occur at higher levels. "How does this effect our commitment to the community" is a question to address. If it isn't official, then is best-effort by the people who pushed for it to go open-source.
An open source maintainer is never obligated to address your bugs / issues. However it is good open source citizenship to be clear about what level of support people can and can't expect.
Officially supported means it's actually owned by some team. They'll dedicate resources to it, meaning it will be accounted for on any project planning or resource management the management needs to do.
Officially supported things tend to be bigger.