His interpretation is flawed. Firstly, he leans on the untrustworthy NIV Bible. Please look up the free PDF book "Serious Omissions in the NIV Bible" by Keith Piper.
Secondly, Psalm 2 is pretty clear in its context.
Psa 2:9 Thou shalt break them with a rod of iron; thou shalt dash them in pieces like a potter's vessel.
Psa 2:10 Be wise now therefore, O ye kings: be instructed, ye judges of the earth.
Psa 2:11 Serve the LORD with fear, and rejoice with trembling.
Psa 2:12 Kiss the Son, lest he be angry, and ye perish from the way, when his wrath is kindled but a little. Blessed are all they that put their trust in him.
The rod is a ruling scepter, it is iron because iron was the pinnacle strong metal at the time; the connotation and context are clear that those who resist the Lordship of the Son will be destroyed.
The rod of iron CANNOT be a shepherd's staff as your author surmises. I have used an iron demolition bar to dig holes and demolish structures. It is very heavy, too heavy for a shepherd to carry around all day. Besides, iron was a valuable commodity in the ancient world; a shepherd would not have a lot of extra iron to be making shepherd's crooks out of. No, a shepherd used wooden implements like we do today for hiking sticks.
Finally, there is THIS:
Rev 19:11 And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war.
Rev 19:12 His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself.
Rev 19:13 And he was clothed with a vesture dipped in blood: and his name is called The Word of God.
Rev 19:14 And the armies which were in heaven followed him upon white horses, clothed in fine linen, white and clean.
Rev 19:15 And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.
Rev 19:16 And he hath on his vesture and on his thigh a name written, KING OF KINGS, AND LORD OF LORDS.
This figure is Christ. He came first as a humble suffering servant. When He returns, it will be as a conquering King.