it broken down so the man --------it

情态动词+have done结构并不一定是虚拟 也有很大可能是表猜测.
mightn't have caught和couldn't have caught的区别在于前者表示未知的猜测,后者表示有预知性的猜测（这要结合具体语境和句子中有无提示性词）,所以这句话的猜测应该是有预知性的,故用couldn't have caught.