For example, the line "Change Segment (key=1021): 1131"
It looks like the "key=1021" is the ID of the segmentation, which you can see in the URL when looking at the segmentation in the Database area: https://app-sjh.marketo.com/#SG1021A1
I assume the "1131" must be unique identifier for the specific segment the lead is being sorted into via that segmentation, but I don't know how to match that number to the segment.
Of course, I can look at what their current value for that segmentation is and whether or not it has changed, but it would be nice to trace it back to the creation activity.
Update: you can't find the segment names via the interface (as far as I can tell), but it's easy to pull via the REST API using the segmentation ID. http://developers.marketo.com/rest-api/endpoint-reference/asset-endpoint-reference/#/Segments
For the above example, GET /rest/asset/v1/segmentation/1021/segments.json
The response matches those IDs, like 1131, to the segment name.