oddly sized 53cm CAAD4T ?

[Shako23]

so i just picked up this 2003 (i think, based on searching the promo catalogues) Caad4T.
I rode the bike around for a while before becoming convinced it was smaller than the advertized 54cm size. I turned the bike over to examine the bottom bracket and saw this:

I havent seen 53cm as an option on any of the Caad4 models offered in Patriot Blue. What happened? Were these bikes available in a custom size?
Thanks!

 

[black lightning 1987]

In the first years of CAAD4, odd numbered sizes were available to be ordered as framesets. Perhaps that continued to be an option in later years but wasn't promoted in the catalogs.