Oh, kinda like Southern Baptists who baptize by sprinkling?
I think they are a breakoff of what we today would consider the PCA (Presby Church of America) due to the PCA’s liberalism. J. Grashem Machen (sp?), renowned as an Ivy League expert in Greek (Princeton?) was among their founders, and also among those who came up with the 5 Fundamentals of the Christian faith, from which the word “fundamentalism” eventually derived.
Since the S. Baptists are primarily a calminian, adult anabaptistic denomination, they are really quite different from the OPC’s solidly calvinistic, reformed faith.