I am not sure the size in relation to medium or large... but it was NOT small. That much I know! I think it was on the larger size, but it was next to several Bantom eggs.
That is good to know what he might be, because I just don't know! He came in an assortment of colorful eggs.
From the sounds of the egg and he looks like ok,
No not a barred rock sorry,
Your chick has black feet, so im thinking black sex link
or black broiler
Some ameraucanas do lay tan eggs, so it could also be an one. sorry i guess im not much help.
but at least you know it may be one of those. LOL