Strange (green) code coming back from the database

I have the following PHP query

$mysqli = new mysqli(HOST, USER, PASSWORD, DATABASE);

$mysqli-> set_charset("utf8");

$stmt = $mysqli->prepare("select header, title, footer, head from configs");

$stmt -> execute();

$stmt -> bind_result($header, $title, $footer, $head);

$stmt -> fetch();

echo $header;

But when I give echo in $header the <?=$teste?> code that is in the database comes as an exclamation and two traces before the interrogation, causing the code not to appear, inspecting with visualization that the variable is in green. Why?