What qualifies as a major overhaul?
"0 SMOH Lower End." means just what it says. The lower end was completely rebuilt but there wasn't a complete overhaul of the "top end". Some of the old top end parts must have been re-used without being overhauled. 

I would suggest speaking to the person who did the overhaul to get more information on why the top end did not qualify for 0 SMOH as well.