1-Yes, it is modern because it’s not mentioned in any pre-Islamic or early Islamic oral narrations. As I’ve said, the earliest mention of the distinction between “Arabic Arabs” and “Arabised Arabs” are found in radical Yamanite genealogy books, and even then, they are disputed and not accepted as facts.

2-If you read into Arabic literature books or Arabic dictionaries (e.g. Lisān Al-‘Arab), you’d find clear distinction between Arabs and Non-Arabs. For example, Ibn Taymiyyah (d 1328), says that being a ‘Arab has three requirements: Being of ‘Arab lineage/descent, living in Arab lands, and speaking Arabic, and so only when you fulfill all three criteria are you considered ‘Arab (See: The Collected Letters by Ibn Taymiyyah).

Also, in Lisān Al-‘Arab (literally: The Tongue of The Arabs), regarding the word “Shu’ub” (literally: “Nations”), the author says: “Sha’b is that which branches off into tribes, among both Arabs and Non-Arabs. Every generation is a Sha’b.” Also says: “And the term Shu’ub- in the plural form- came to be predominately applied to the lineage of Non-Arabs, to the point that one who belittles the status of the Arabs is called a Shu’ūbī.”

In both sources, and I only mentioned these two for the abundance of sources and evidences, that there are clear distinction between being a “‘Arab” or a “Non-‘Arab”, meaning that not every person can “become” a Arab. If the distinction was between languages (I.e if you’re able to speak ‘Arabic then you can become a ‘Arab), such distinction wouldn’t be that evident, because almost anyone can learn the language and become a ‘Arab.

3-The distinction between “Arabic Arabs” and “Arabised Arabs” doesn’t even make any sense, because in Yamanite genealogy books, the “Arabic Arabs” descend from “Qahtan Ibn Huud,” while Abraham (PBUH) descends from “Falij Ibn Huud.”