Who signs executive orders? ... Yes, the president does.
Have you read the EO?
If the President could arbitrarily declassify any classified information, why would it be necessary to refer it back to the originating agency or establish a procedure for them to appeal the declassification?
Does it make sense that any President can divulge sensitive, classified information to a foreign power and can escape prosecution because he can automatically declassify it? No man is above the law, even the President.