I think fill factor and microlenses may also pay a major role. Increasing the fill factor reduces aliasing.
Tried both files in rawtherapee, there I can't see a small difference but not that kind of difference in aliasing. Color aliasing artifacts depend a lot on demosaicer. It also depends a lot on the exact positioning of the pixels in relation to the object.
My theory is that there's a very slight difference in offset where the "pixel grid" comes over the bars, and the IQ280 just got unlucky and got in a worse position than the IQ250, and this got enlarged by the demosaicer.
So I don't think the IQ280 is any worse in this regard. I haven't analyzed it in detail though.