Yes, the Irish were slaves as well. But the point is not that they were also enslaved, but how the nature of slavery became tied to "race." The case of Obama's ancestor John Punch (on his supposedly-white mother's side) was key in this transformation. The "negro" John Punch escaped with two other "indentured servants" who were white. When they were captured, a very disparate sentence was imposed on each:

"Whereas Hugh Gwyn hath by order from this Board brought back from Maryland three servants formerly run away from the said Gwyn, the court doth therefore order that the said three servants shall receive the punishment of whipping and have thirty stripes apiece. One called Victor, a Dutchman, the other a Scotchman called James Gregory, shall first serve out their times with their master according to their Indentures, and one whole year apiece after the time of their service is expired by their said indentures in recompense of his loss sustained by their absence, and after that service to their said master is expired, to serve the colony for three whole years apiece. And that the third being a negro named John Punch shall serve his said master or his assigns for the time of his natural life here or elsewhere."

(General Court of the Governnor's Council 1640).

This was a pivotal case in making slavery in America an inherited condition, based on the fantasy of "race." It was that tie between the economic condition of slavery and the prejudice of race which made the American institution of slavery substantively different.

The important question is not whether Irish were ever "slaves," but what they learned from that enslavement. Unfortunately, too many of them failed to appreciate that lesson, and instead succeeded in bringing us our first, and explicitly racist, immigration law.

https://medium.com/the-audacity-project/an-anti-racist-hero-is-something-to-be-8e522f05276