It does not evaluate to true, it gives you the feedback of the ajax call, which you can use for true or false analysis.
Ajax request http://somesite/index.php?update=addDBthingy tag "updating"
On your server, when the php script has run, it might echo back the result of the adding, for instance echo "success";
Then, in C2, when you have
On request complete "updating"
compare 2 variables
Ajax.LastData = "Success"
action set some boolean = true
action set some boolean = false