Washing of Hands Practised by “All The Jews”?

In Mark 7:2-4, we read the following passage:

Mark 7:2-4

2 And when they saw some of his disciples eat bread with defiled, that is to say, with unwashen, hands, they found fault.

3 For the Pharisees, and all the Jews, except they wash their hands oft, eat not, holding the tradition of the elders.

4 And when they come from the market, except they wash, they eat not. And many other things there be, which they have received to hold, as the washing of cups, and pots, brasen vessels, and of tables.

There is a problem with this passage, however: the ritual washing of hands was obligatory only on the priests!

This is attested to by Nineham when he says that:

…the evidence of the Talmud is that in the time of Jesus ritual washing of hands before meals was obligatory only on the priests.Dennis E. Nineham, Saint Mark (Penguin, 1963), p. 193

So clearly we have Mark confused with the “…Jewish practise of his own time with the Palestinian practise of forty years ago.”Randel Helms, Who Wrote The Gospels? (Millenium Press), p. 10

It is hence because of this historical error by Mark which is why many scholars of the New Testament concluded that Mark was probably not Jewish. This is echoed by McDonald and Porter, who says

Essentially, the arguments against John Mark, a Jewish resident of Jerusalem and later the companion of Paul and also of Peter, writing this Gospel are that he does not appear to be familiar…with Jewish customs, overgeneralizes about the Jews (7:3-4), from whom he seems to distance himself…Lee Martin Mc Donald and Stanley E. Porter, Early Christianity and its Sacred Literature (Nov 2000, Hendrickson Publishers, Inc.), p. 286

Bart Ehrman, the renowned New Testament scholar and textual critic, further elaborates on the matter by stating that

…in 7:3-4, where Mark has to explain the Pharisaic custom of washing hands before eating for ceremonial cleansing. Presumably, if his audience were Jewish, they would have known this custom, and Mark would not have to explain it. What is even more intriguing is that fact that Mark appears to misunderstand the practise: he claims that it was followed by “all the Jews.” We know from ancient Jewish writings that this is simply not true. For this reason, many scholars have concluded that Mark himself was not Jewish.Bart D. Ehrman, The New Testament. A Historical Introduction to the Early Christian Writings (2nd edition, Oxford University Press, 2000), p. 74

So the question remains, if the author was a native of Palestine and a Jew, then how was he ignorant of the Jewish customs and made such a fundamental error regarding a practice that was only limited to Jewish priests?

And only God knows best!