He was when he tried to leave. The Laws of the State in which he was held in bondage recognize him as such I am sure. That brings into effect the above provision from Article IV.
Prior to the Scott decision State courts in Slave States did in fact award freedom to slaves in cases identical to Scott's. Taney ignored that president
The "precedents" set by state courts are not binding on the Federal Courts, which I would say have jurisdiction in the case of Dred Scott and a dispute between states.
and then went even further overturning the Northwest Ordinance and the Missouri Compromise,
Nothing but a constitutional Amendment can nullify the effect of article IV. No "ordinance" and No "compromise" can render inoperative that clause.
and then somewhere divining that the Framers did not intend people of African descent to become citizens even though those framers themselves recognized such people as citizens.
And I agree with you that he erred there. I know of about a dozen Black Citizens from the revolutionary war period. Yes they were recognized as citizens, and therefore Tanney was simply projecting his own incorrect opinion.
But the larger holding was legally correct for the time. It wasn't overturned with a subsequent Supreme Court ruling, it was overturned by the passage of constitutional amendments that rendered that decision moot.
Scott did not attempt to leave anywhere. He did not run away or even attempt to run away. The State circuit court, in a slave state said that based on the facts of the case, Scott was free. He never tried to run away and the Fugitive Slave Clause never was a factor in the case.
You still don't comprehend what the case was about and why Taney's decision was such a disaster.