The article doesn't mention which son Abraham offered to sacrifice, perhaps because it conflicts with the story in the Bible. According to Muslims, Ishmael was the chosen son. Here's an extract from a Muslim sermon given this past month:
‘Eid Al-Adha’ is a symbol of obedience. It signifies submission to Allah. On this day, we commemorate together the acts of obedience and submission performed by Prophet Abraham and his family when he was commanded to take Hajar and their son Ishmael to an uninhabited, barren, distant land and leave them there alone. He submitted and obeyed. When Hajar realized what was happening, she cried out, “Abraham! Are you going to leave us in this valley where no people live?” She repeated the question yet she received no answer, so she asked him, “Did Allah order you to do this?” He replied, “Yes.”
So she said, “Then Allah will not let us perish.” Thus she submitted. Furthermore, when his son Ishmael became older, Abraham received a command from his Lord to sacrifice him. He submitted and so did his son. The family of Abraham was a family of obedience and submission. They were tested and tried again and again, but the result was always submission and obedience. Both ‘Eid al-Adha’ and ‘Eid al-Fitr come after performing a pillar of Islam and an act of obedience. Hence ‘Eid Al-Adha and ‘Eid al-Fitr are annual reminders that this life is a test and we must be obedient if we wish to be successful.