Yep, it's absolutely possible. If you get a little pre-ignition bump, they will run backwards. There are all kinds of reports on the internet about it happening (the 2-cycle can run backwards by design) and I even had it happen to me with my old Ryobi weed wacker.
Here's a link to a discussion about it...
Ryobi trimmer runs backwards - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information