The jquery ui tooltip, by default, requires that the elements on which it pops-up have a title attribute
(this is how jquery ui knows which elements to bind the event to). The first line of this code:
$chart.attr( "title", content )
.tooltip({position: evtPos,
content: content})
.tooltip( "open" );
is setting that attribute and is what you are seeing in your screenshot.
If you change it to:
$chart.tooltip({position: evtPos,
content: content,
items: '*'})
.tooltip( "open" );
this should still allow the tooltip to popup without the title
text. Fiddle here.
To be honest I find that code sample very obtuse. You'd be better served following this example in the flot documentation.