Mysqli simple query: weird result using mysqli_stmt_bind_result - php

Question

I have a mySQL table defined as:
CREATE TABLE IF NOT EXISTS `tweet` (
`user_mail` varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
`date_sent` datetime NOT NULL,
`date_edited` datetime NOT NULL,
`message` tinytext CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
PRIMARY KEY (`user_mail`,`date_sent`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
And two differents entries in this table as follows:
INSERT INTO `tweet` (`user_mail`, `date_sent`, `date_edited`, `message`) VALUES
('RichardSpencer#gmail.com', '2016-01-22 14:07:45', '', 'First tweet !');
INSERT INTO `tweet` (`user_mail`, `date_sent`, `date_edited`, `message`) VALUES
('JohnDoe#gmail.com', '2016-01-22 14:07:45', '', 'Second tweet !');
I'm using this PHP function to retrieve all tweets (at this moment there are only 2 tweets) of my table 'tweet'
function getAllTweets($con, $limit){
$stmt = mysqli_prepare($con, 'SELECT * FROM tweet ORDER BY date_sent DESC LIMIT 0, ?') or die('Oups erreur dans la requète SELECT avec le message: '. mysqli_error($con));
mysqli_stmt_bind_param($stmt, 'i', $limit);
mysqli_stmt_execute($stmt);
mysqli_stmt_bind_result($stmt, $datas['user_mail'], $datas['date_sent'], $datas['date_edited'], $datas['message']);
while($datas == mysqli_stmt_fetch($stmt)){
$result []= $datas;
}
return $result;
}
And I'm calling this function like this:
$allTweets = getAllTweets($con, 99);
When I see var_dump($allTweets);I get 2 tweets as I was especting but Both results are the same tweet . . . here is the var_dump result
array (size=2)
0 =>
array (size=4)
'user_mail' => string 'johnDoe#gmail.com' (length=17)
'date_sent' => string '2016-01-22 17:25:34' (length=19)
'date_edited' => string '0000-00-00 00:00:00' (length=19)
'message' => string 'Second tweet !' (length=14)
1 =>
array (size=4)
'user_mail' => string 'johnDoe#gmail.com' (length=17)
'date_sent' => string '2016-01-22 17:25:34' (length=19)
'date_edited' => string '0000-00-00 00:00:00' (length=19)
'message' => string 'Second tweet !' (length=14)
If you see my table I should have one tweet with the message "First tweet !"
And a second tweet with a message "Second tweet !"
Where is my mistake ?