My guess is somewhat blander.

1. Anon breaches laptop, finds UDIDs.

2. Anon tells other anons he got the UDIDs from a laptop.

3. Other anons tell more anons it was a government laptop.

4. Release group writes "FBI laptop" in their pastebin.

(5. ??? --> 6. Profit!)

The heterogeneity and disorder in Anonymous (at least it was like this back in the day) means that the chain from leaker to releaser -- usually passing through several people and IRC channels -- plays out a bit like a game of telephone. This serves to protect the leakers, but it can mess with some of the details.