Yes, you are correct. IPC-7351C introduced contoured courtyards. IPC-7251 also allows contoured courtyards for through-hole components.
Replace the word "rectangular" above with "polygon".
Sorry for any confusion that might have caused.
Neither standard elaborates on the electrical aspect of this clearance but my interpretation is that it refers to the clearance between the bodies of two adjacent components that may be conductive, or become conductive with contamination, as well as the clearance between the body of one component and the land pattern of another.
The copper-to-copper clearance requirements are usually selected according to manufacturing limitations but in practice the clearance between tracks and lands (pads) is usually greater in order to ensure the track is covered by solder mask.
Just my interpretation, yours may vary.