I don't agree. Class::DBI is not a generic term. It is a specific and well-known module. Anyone seeing Class::DBI::Lite on CPAN would reasonably assume that it had something to do with Class::DBI.
No one complains about things like CGI::Simple because CGI is a truly generic term. Is it ethical for people to grab generic namespaces for things like CGI or Template? Maybe, maybe not, but that doesn't change the issue here. Personally, I think it would be better to have called XML::Parser::Lite something else, even XML::ParserLite, in order to keep it out of the same package namespace.
Incidentally, I don't think Class::DBI could reasonably be called heavy.