How to check with update trigger if only one column was updated postgresql
Instead of using the value "syncstatus_yes", you could use your Syncstatus column to store a binary code that represents the columns you are updating.... and then move the syncstatus as it is to the log. This way you will know exactly which columns you are syncronizing... 

whether you use your app code or either the trigger OLD and NEW values, you can know exactly which columns are being updated. Then you can use those columns to build your Syncstatus column

For example: (suppose you have 6 columns + syncstatus column)

Syncstatus = 19 = 010011 = power(2,(6-2))+power(2,(6-5))+power(2,(6-6)) 


this means that columns 2, 5 and 6 are being updated.