nope, says its an urban legend in the Uk and disproved in the US
Hoof-position symbolism
"Equestrian statue of Confederate General James Longstreet on his horse Hero in Pitzer Woods at Gettysburg National Military Park, Gettysburg, PA
In the United States and the United Kingdom, an urban legend states that if the horse is rearing (both front legs in the air), the rider died in battle; one front leg up means the rider was wounded in battle or died of battle wounds; and if all four hooves are on the ground, the rider died outside battle. For example, Richard the Lionheart is memorialised, mounted passant, outside the Palace of Westminster by Carlo Marochetti; the former died 11 days after his wound, sustained in siege, turned septic.
In the United States, the rule is especially held to apply to equestrian statues commemorating the American Civil War and the Battle of Gettysburg, but there are at least nine instances where the rule does not hold for Gettysburg equestrian statues. One such statue was erected in 1998 in Gettysburg National Military Park, and is of James Longstreet, who is featured on his horse with one foot raised, even though Longstreet was not wounded in battle. This is not a traditional statue, as it does not place him on a pedestal. One writer claims that any correlation between the positioning of hooves in a statue and the manner in which a Gettysburg soldier died is a coincidence.