M&S use the phrase I noticed. I think it must be of American origin. Can't think how else they'd have dug up the description. If the chicken in breadcumbs wasn't tender I'd be having some words with them.
Bits of chicken in breadcrumbs are goujons as far as I'm concerned.
I've just checked the M&S website and their 'tenders' are listed as 'chicken breast' not particularly the part called 'tenders'.