You can't know, but you can make a pretty good guess from the preponderance of the evidence. I think it's a virtual certainty that Rawle made this, and every other argument of which he could think, in an effort to secure the freedom of Flora.
I read a lot about Rawle at the time I was researching all this, so I may have reasons for my impressions that I can no longer find the supporting material to cite. It's been about a decade since I was looking at Rawle.
In fact, looking at some of my old research, it was in 2013.
Unless you actually have something which shows Rawle saying 'I argued for X', your virtual certitude here is impossible. All extant sources remarking on this case indicate that Flora's counsels argued that slavery itself was incompatible with the constitution of Pennsylvania based on the following clause:
A good lawyer puts forth more than one argument. With three of them on this case, and one of them being Rawle, who asserted in the future that Citizenship is given by birth, it is reasonable to believe this argument was made in 1805.
In any case, Rawle was around when that Digest of Select British Statutes was published and promulgated throughout the Pennsylvania legal system, and so he knew that his view was wrong according to everyone else in the legal system in which he worked.
See? Here I am arguing for your "precedent" idea, in the Pennsylvania court system of the 1800s.
To assert, as you have, that Rawle "was trying to abolish slavery by making slaves into citizens", insofar as this case is concerned, is not supported by the available evidence.
Read more Rawle. You can start with this.
Again, you assert this without evidence: nothing available indicates that Rawle tailored his anti-slavery arguments with regards to citizenship, instead of regarding more fundamental ideas regarding all men being born "free and independent."
and one of them being Rawle, who asserted in the future that Citizenship is given by birth
One does not tie into the other. Even an overview of Rawle's 1825 work "A View of the Constitution of the United States of America" does not display any indication that he held slaves to be citizens due to being born in America (at least none which I've been able to find). One can believe that slavery is immoral, and that the slaves deserved freedom, without then claiming they therefore qualified as citizens.
See? Here I am arguing for your "precedent" idea, in the Pennsylvania court system of the 1800s.
You've not even gone that far, because you haven't actually provided any precedents of Rawle's to look at to support your assertion.
Even the document you linked to was a eulogy delivered about Rawle after his death; it does not intimate whatsoever that Rawle's ideas about birthright citizenship were tied or influenced by his opinions about slavery. As a matter of fact, the eulogy itself states the following on page 24, providing a motive for Rawle's efforts as an abolitionist (bold is emphasis mine):
"For such devotion there can be but one motive, and that is, humanity; there can be but one recompense, and that is the blessing of the bleeding and broken heart, upon which the soul shall be wafted to the bosom of its God. His doctrines upon this subject, which were the doctrines of Franklin, of Lafayette, of Rush, of Wilberforce, may be scoffed at by some—condemned by others—they may not have been safe doctrines to live by, but they were safe to die by; and, for my single self, I should ask no prouder inscription for my humble tomb, than - HERE LIES THE FRIEND OF THE FRIENDLESS AFRICAN."
Again, as previously supported by other sources cited: Rawle's animus against slavery was seemingly tied to more fundamental beliefs about the common man. Nothing cited by you or myself supports the contention that his ideas about birthright citizenship were motivated by his anti-slavery fervor.