Once sent classified, they remain classified.The documents were not properly marked and therefore cannot be held responsible for being aware of the markings.
Furthermore, the emails in question did not contain confidential information as the State Dept said.
Your snipped refers to different emails that were "classified at the time they were sent" but not indicated that they were classified.
My Factcheck.Org snippet ( official, approved truth source of the left) also said some were at the level of what Trump had.
More than 2,000 of the 30,490 emails Clinton turned over to the State Department contained classified information, including 110 emails in 52 email chains that contained classified information at the time they were sent or received.
(Most emails were retroactively deemed to contain classified information by the U.S. agencies from which the information originated.)
“Only a very small number of the emails containing classified information bore markings indicating the presence of classified information,” Comey said. “But even if information is not marked ‘classified’ in an email, participants who know or should know that the subject matter is classified are still obligated to protect it.”
Regardless, Trump should be afforded the same 'privileges.