It is possible that whoever the informant was for Sabert S. Offutt's death certificate had incorrect information about who his parents were. It is also possible that the information on his death certificate was written down wrong for the Deaths with Burials book--that's why you may want to double-check by getting a copy of the death record and seeing for yourself what it says.
You may also want to get a copy of his obituary to see what it said--it apparently was in the July 12, 1945 issue of The Republican (a
Danville newspaper). The
Danville and Plainfield libraries both have the Republican on microfilm and could get you a copy of his obituary.
One other thing--for what it's worth, the index of Greenlawn Cemetery only had one other
Offutt listing, but the first name was not Alexander, but
Lorenzo (no dates). Perhaps it was a footstone or something, where it was hard to tell which family group it belonged to?