Can be seen to be fiction as it would have been difficult to sneak something into the chambers of the Roman general as the room would have been heavily guarded
Political sense: supporting Cleo meant he could force Ptolemy and his advisors to work harder to earn JC's trust and support, Caesar needed Egyptian resources and wealth for success back in Rome - Cleo is a better friend to Rome than Ptolemy
Caesar and Cleo sailed down the Nile on huge barges in front of their citizens so people who are not in major cities could see them - showed wealth and power of Ptolemaic dynasty