Why was Amr ibn al-'As nicknamed "Son of the Most Generous"?

The phrase "Ibn al-Akramin" was not a title for Amr ibn al-'As (may Allah be pleased with him). Rather, his son Abdullah ibn Amr said it, and it was not a title for him, but rather a praise for the Arabs. The Prophet (peace be upon him) was praised with it in the words of Sawad ibn Qarib: "And verily you are the closest of Messengers in means... to Allah, O son of the most noble, the goodly ones." It has been used in other contexts for praise.