All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
This statement indeed implies religious violations. If we consider its apparent meaning, then we say that Muslims are not called "believers" because of the reason mentioned. In fact, they are called believers because they believe in Allaah, His angels, His Books, His Messengers, the Last Day and the predetermination, the good and bad of it.
If we take it to mean what he intended, it still makes an unacceptable generalization. Not all Muslims believe and spread false information without verifying it. Hence, it is wrong to make such a statement, whether jokingly or by way of criticism.
The believer should be cautious about the words he says so as not to say what contravenes the Sharee‘ah. Allaah The Almighty forbade us from using ambiguous words that carry an apparent good meaning and an implied corrupt one; Allaah, The Exalted, says (what means): {O you who have believed, say not [to the Messenger of Allaah], "Raa‘ina" but say, "Unthurna" and listen. And for the disbelievers is a painful punishment.} [Quran 2:104]
Al-Qurtubi commented on the verse saying, "Ibn ‘Abbaas related that Muslims used to say to the Prophet, sallallaahu ‘alayhi wa sallam 'Raa‘ina', meaning, 'listen to us', or 'give us your attention.' However, in the language of the Jews this was an insult, like saying 'Listen! May you not listen!' The Jews took advantage of this and said: we used to insult him in private, now we can insult him in public. Therefore, they started saying that word to the Prophet, sallallaahu ‘alayhi wa sallam, and laugh among themselves. Sa‘d ibn Mu‘aath knew their language so he said to them, 'May the curse of Allaah be upon you!' If I ever hear any of you saying this word to the Prophet, sallallaahu ‘alayhi wa sallam, I will strike his neck!.' The Jews replied, 'Do you not use the same word?' Thereupon, the verse was revealed (commanding Muslims not to say Raa‘ina but to say Unthurna [i.e. Do make us understand]); Muslims were forbidden from using the word so that the Jews would not imitate them and use it while intending its corrupted meaning." [Tafseer Al-Qurtubi]
It is not necessary that this person had made this statement with the intention of mocking the believers. He may have intended to offer advice to those who do so (i.e. those who believe and spread false information without verification) and guide them to the correct path, but he made the wrong choice of words.
Allaah Knows best.