How does my dual core i5 in my MacBook Pro have more than 400% CPU usage?
If you look here, you have 2 cores that can execute 2 threads each with turbo boost.  So I would assume 400% is your maximum.  Seems likely that Adobe maxed out one CPU completely, and the other CPU was running the OS and other tasks.

The additional usage may be because your 2.7 ghz CPU was turbo boosted to 3.1 ghz at the time.

Also, within Activity Monitor, you can choose Window -> CPU History, and it will break down everything.  For example on my 6 core Xeon, I have 12 graphs.