I had developed a domain in May 2007 , but suddenly in February 2008 (last month), I saw some UV stats and clicks in my Sedo account for that domain. I had not made any changes in Name server information for the domain.

Is it possible for anyone to change name server information from my control panel without my knowledge?
The archived actions from my control panel do not show any changes in name servers.

You can access the sedo parking page also this way:

http://www.sedoparking.com/domain.com/

where domain.com is your domain name. That could be how you got your visits and clicks.

What I find surprising is that all the traffic for that domain was for just 2 days, when there was a big DDOS attack on my other sites.

If it was normal human traffic , it would be more uniformly distributed over the last few months.