Are you sure we're talking about the same thing? Right out of the box frescobaldi's "music view" (you know, the one with the cream background that sits alongside the "code") is most certainly a 72dpi rasterized bitmap-looking version of the score.
If that’s true, then the bitmap is generated anew for every zoom level, screenshot attached.
But the changelog states that Retina display support was added only in 3.0.0, so maybe that’s your issue.
