Meaning of 他是以朋友說這番話的
The sentence should be interpreted as 他是以一个...老朋友(的身份)说这番话的, means he said that as a ... old friend.

And from 一个在中国生活了将近六十年的老朋友 we can tell that 艾黎 has been lived in China for 60 years nearly.