no you are not. You are using @Kevinkun's Tableviewer extension
As I previously advised you:
"You may want to look at the example aia project provided by the extension developer..."
To solve your issue, you would need to make a call to the data that will return the header row, which you can then use with your filtered data.
If you use gviz to return filtered data from your spreadsheet, this will include the header row.