I can't explain the reasoning behind Joseph 'Manger" being listed as a head of household except that maybe he was listed with his parents, but they were on one page and he was on the next one (? - I'm only guessing at this). Therefore, it would appear that he was in a household by himself (or with any siblings that were born after him) and, as such, was listed as head of household. I will try to get up to Hayward to see if I can find this info for you. I'll get back to you on it when I do.
In regards to Joseph Norman not being born in Hayward because he was not listed in the pre-1907 birth index, I want to remind you that there was no state law in Wisconsin prior to October 1, 1907 stating that births, marriages or deaths had to be reported or recorded by county or state officials. It was completely up to the doctor or the family if that info was reported. So he COULD have been born in Sawyer Co., but just not reported as having been. That's the hard part about doing the early research. Thankfully you were able to find the baptismal record! I don't know if his parents were still alive at the time of his baptism, but I will check to see if I can find any death records on them while I am in Hayward also.
Hope this helps to explain things a little more. And I hope to be able to fill in some more blanks for you.