It could just be the sequence with which the birth info came in for recording. Some hospitals might not get them in right away, some parents are not ready with a name right away, so it holds it up for a couple. I am not sure this serial number question is important.
Indeed, the paperwork could easily have been processed out of sequence. No biggie there.
HOWEVER, this now gives us good photos of what a REAL birth certificate, issued just minutes before his, looks like. Now we know what we’re looking for!