Bet this won't stick.
I think you're right. When you separate from the service, you're supposed to go through your DD-214 with a fine-tooth comb because it's the most important document you posess from you time in the military.
While it speaks volumes for Kerry's attention to detail, this is going to be an easy one to explain away. Some clerk at a PSD somewhere transcribes awards received onto the DD-214 straight from the member's Page 4's in their original service record. So, the award was either transcribed incorrectly from his Page 4 or it was mis-typed (the Bronze Star is directly above the Silver Star on the DD-214).
Judging from the mushroom clouds spotted over the wreakage of the Kerry campaign, I don't think it matters.