Actual displacement vs motor size designation is pretty common within the industry. The 396 GM big block comes to mind as yet another example of advertising vs reality with cid.
Whats under the hood? I recall in the late 60's early 70's, with GM car's in particular, you could never be sure WHAT you might find under the hood. A Buick or Pontiac motor in a Chevy, or vice versa. It was a big stink when people bought a brand name car and then discovered a different brand name motor under the hood.
Hey, at least Shelby was 'keeping it in the Ford family'.