The domain search facility there is fantastic. I have my own domain and try to use a different email address for every signup. Luckily that site allows you to do a complete search for @example.com in the 'domain search' tab.
CS5 was released in April of 2010. The update CS5.5 was released in May of 2011.
I'm guessing someone used your email address to start a free trial in order to pirate the software. They were either replacing an older version they had, or wanted a free upgrade and attempted to hide their identity.
FYI Photoshop is one of the most pirated pieces of software.
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