Those guns are probably for the Battle of Nagashino a year later, where Oda and Tokugawa are said to have annihilated the famed Takeda Cavalry by setting up bamboo barriers behind which they fired musket in succession, breaking their charge. If you play Fate/GO that's the story behind Nobunaga Noble Phantasm, the Three Ranks Fire. That is also the final battle of Kurosawa's Kagemusha.