Yesterday I was at Edinburgh Castle. Where an author was telling the tale of the Crimean War focusing on the 93rd Highland Regiment. He made it seem that Campbell's strategy was to make the Russian cavalry believe it was a trap. Before that I heard that it was because Campbell had a very low opinion of the Russian cavalry. Did the man exaggerate to make a better tale?
The only answer you're likely to get here is "We don't know". The decision to form line two ranks deep is contrary to any and all military sense. To my knowledge Sir Colin Campbell never commented on why he issued the order. Is it possible that it was his lack of respect for the quality of Russian cavalry? Sure. Did he ever publicly state that this was the case? Not to my knowledge.
By all rights what should have happened is that the Russian cavalry smashed through the center of the 93rd, routing them and opening the way for 2000 more cavalry to pour into the British camp instead of engage the Heavy Brigade.
An equally plausible explanation to why he acted the way he did is that he took stock of the situation and judged that with the terrain as it was the formation of two ranks would allow him to bring maximum firepower to bear against the enemy.
While the first volley was observed to be ineffective (fired at around 600 yds), the second volley, supported by cannon fire, was more effective and caused the cavalry to veer left (350 yds) the third volley (150 yds) by the grenadiers under Ross was very effective and caused the Hussar to continue their left turn and abort the charge.