Lorgar was never in command at Calth. As far back as the Index Astartes articles it was Kor Phareon who led the attack whilst Lorgar was elsewhere.
Here's the original text and description of the Battle of Calth from the Word Bearers Index Astartes article.
"When the Word Bearers launched their attack against the Ultramarines, the strike against Calth was led byone of Lorgar's greatest champions, the former Master of the Faith, Kor Phaeron. This mighty champion swore to utterly destroy the planet, and was very nearly successful.
From his personal battle barge, now renamed Infidus Imperator, Kor Phaeron directed a full-scale invasion of the Calth System. Calth's three sister planets were all destroyed, massive geo-nuclear strikes ripping them apart at the core. Its once gentle sun was laced with deadly metals and substances that increased the star's radiation output tenfold. Within a century after the Heresy's end, the final elements of Calth's atmosphere were burned off, the world left airless, its populace now dwelling in gigantic underground caverns.
Upon its surface, the Word Bearers fought the Ultramarines to a standstill. The traitors held superiority in numbers, weaponry and brutality, but the Ultramarines would never give in. As driven as the warriors of Lord Kor Phaeron were, they could not dislodge the Ultramarines, many of whom had once called the planet home.
The war upon Calth was devastating and horrific. Ancient codes of warfare and martial conduct were broken and set aside by the Word Bearers as all manner of death and destruction was unleashed. The Ultramarines were stunned by the millions of cultists the Word Bearers used as human shields and disgusted by the hordes of daemons unleashed as shock troops. The Word Bearers, in turn, had underestimated the tenacity and resolve of their hated foe.
In the end,Lord Kor Phaeron was defeated when reinforcements from Macragge drove the Word Bearers from the surface of Calth. Kor Phaeron retreated all the way to the Maelstrom, a turbulent region of the galaxy where the Immaterium of Chaos seeps through into the material realm of the universe. The Ultramarines were victorious, and their leader,Brother Captain Ventanus, would one day set foot upon a broken Colchis, symbolically capturing the abandoned home world of the Legion that had once threatened to enslave Ultramar.
While Kor Phaeron set his men upon Calth, Lorgar was leading the rest of the Legion against Terra."
So you see Know No Fear is actually rather faithful to the original source material.