One thing i could say is, both the repeater and flexible content fields save their data in this format:
$ParentName_$RowNumber_$ChildName
the values of testimonial for the first and second row are saved into this 2 DB-Fields.
'testimonials_0_testimonial' //for first row
'testimonials_1_testimonial' //for second row
maybe that help.
else: debug $rows => that means: look what inside $rows is.
echo '<pre>';
print_r( $rows);
echo '</pre>';
probably it is not array like you expect (because each subfield has it own db-row)