I have a feeling the lone holdout and possibly other jurors don't know the actual definition of "hearsay" evidence and are conflating it with "circumstantial evidence."
When the "hit man" sat in the witness box and told that jury what Drew Peterson asked him to do (i.e. for $25K find someone to murder Kathleen), that was not hearsay. That is direct evidence (i.e. witness and a party to the conversation).
When various people heard Drew Peterson make comments about how much better his life would be if Kathleen would just die, that too was not hearsay. They heard it directly from the defendant's mouth.
Further, the autopsy and condition of Kathleen's body was not hearsay. That is circumstantial evidence. The bruises are there and can be seen. It doesn't require someone else saying that someone told them Kathleen had bruises all over her body--the photos, the body, the autopsy report-- none of it is hearsay.
While yes, there was some hearsay testimony allowed, there wasn't ONLY hearsay testimony. So to say only hearsay evidence got him convicted implies they gave no weight to the hit man testimony or anyone else who interacted directly with Drew Peterson, and they didn't look at or consider evidence about the state of her body, how it appeared in the tub, what was there, what wasn't there, etc.
If the jury doesn't understand the meaning of "unanimous" I guarantee they don't understand the difference in types of evidence. But... at least they made the right decision even if they're not quite sure what they were looking at in terms of evidence.