I had not seen this event prior to this morning. Is this something new with SP1 or have I just been missing it? It happened during the NTA maintenance window, is NTA responsible?
That is coming from NTA. I can't remember for sure, but I think it was added during the last (or maybe previous) NTA service pack. You can change the maintenance options for NTA in the admin page under Settings | NTA Settings. There is a database maintenance settings section where you can configure how often the compress database and log files frequency.