Peculiar to them unless you count: Delaware, Kentucky, Maryland, Missouri, and West Virginia the slave states who did not secede and where it was legal until the 13th amendment was ratified about four months before the end of the war!!!!
The term came from the southern leaders, John C. Calhoun and Alexander Stephens in particular, who used the term peculiar in terms of “our own” as in our own (southern) institution. It was not a reference to peculiar as meaning strange. The states that did not secede were considered to be southern states. West Virginia seceded from Virginia and stayed with the union.
The 13th Amendment wasn't ratified till December, 1865, some months after the war ended.
When it did go into effect, it freed slaves only in KY (around 50,000) and DE (around 200).
All other slaves in America (98.75%) had been freed before the war ended either by the Emancipation Proclamation or state action.