No problem. Great question once again.
Here's my answer:
The reason why I said he was a "Gentile" is because Abraham wasn't under the Law. It was given to Moses. This was a different covenant given to Israel.
Here's my deeper thoughts on this:
Hebrews are descendants of Abraham, but Jews are given a different classification.
Romans 2:
28For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. 29But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God.
The reason why I brought this up in the first place was because I was under the impression you were looking into the original covenant that was given to Abraham.
What's actually quite intriguing is that one could make the case the "New Covenant" is actually the "Older Covenant" that was given to Abraham before the Law was given to Moses.
The promise was given to Abraham and through Abraham his ONE offspring, which is Christ. We are in Christ, thus the promises are yes and amen for us in Him.
Galatians 3:15To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified. 16Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ.
17This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. 18For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise.
So why did the Law come later if it didn't change or annual the covenant with Abraham? Because the only was to have access to the covenant with Abraham was through Christ. He is THE Offspring.
19Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary.
I hope this answers your question, but just to summarize. Abraham is a Hebrew (by blood), but a Gentile because he was never under the law. And we Gentiles who were not given the Law through Moses come in through the promise of Abraham. So the Law written on stones was never given to us. I already addressed in my previous post how the Law still affects us Gentiles (those without law) because without Christ we are a law unto ourselves. And by this all without Christ will be judged by God. And as Paul says none are righteous, but Him.