he was reported to have covered 30 miles on foot that day.为什

因为在report之前,他走了30 miles,这里有个时间的先后顺序.在报道之前,他就已经做了某件事,所以用了完成时.
译：据报道,那天他步行走了30公里.
也可以改成下面的,或许会更好理解.
It was reported that he had covered 30 miles on foot that day.
实际就是一种过去完成时,不过因为前面有个to,所以这个信息被隐藏了,只能用to have done,看不出来了.
而我下面的句子就用的完成时,就是为了让你能方便地看清楚.