The devil is in the details - the implementation, more specifically. IB can be overwhelmingly liberal in its viewpoint, or it can be not much different from standard American high school fare - it really depends on the people implementing it in a given school.
Anyway, what this article isn't telling you is that the real reason that Woodson High in Fairfax dropped IB is not because of any politics or political views in the curriculum, although that may have played a small part for some parents. The real reason it got dropped is that parents discovered that it simply doesn't translate into as many college credits as a similarly structured AP program, particularly at UVa. and other in-state schools. That's it. No grand political agenda or anything, really.
I don't know why that school dropped IB, but my daughter has an IB diploma from a school in Florida and her IB and AP credits transferred to UVA almost equally.
I thought the IB program was excellent. We were in an "A" rated high school here and still, the IB kids were by far the best in the school.
The only liberal aspect of the program turned up when mine got to UVA and when I questioned how she was spending some of her money, she promptly informed me that we needed to develope a "community of trust." ;)