Were the 2007 'Oh, By the Way' vinyl box set pressings from original analog masters?

No — the 14 albums in the 2007 Oh, By the Way box set were cut from the 2003 digital remasters, not the original analog tapes. Those remasters were the same ones used for the SACD and CD releases of that era, which were sourced from high-resolution digital transfers. So while the 180g vinyl itself is well-pressed and quiet, the sound is a digital representation of the original analog recordings.

Do they sound superior to earlier CD releases? That depends on what you value. Early Pink Floyd CDs (like the 1980s Harvest/Capitol issues)