Translation:The neighbor explains that he is alive.
It isn't just a joke. This article says that 14,000 Americans have to prove that they're alive each year: www.california-disability.com/Articles/It-s-No-Joke-Proving-You-re-Alive-to-the-Social-Security-Administration.shtml
This makes perfect sense to me. I have a 95-year-old neighbor who flies off to the Brooks range in Alaska as soon as the ice on the lake breaks up enough for a float plane to drop him off in total isolation. Every time I ask how he is doing I get the same answer, "I'm still alive."
I can't find the original, but I suspect that it was one person (el vecino) explaining that someone else (a man not in the conversation) was still alive.
So, as an example, when the house of my 92 year old neighbor burned a few months back no one knew if the old guy had been inside. It wasn't until another neighbor called around and found out that the old guy had been staying with his son that anyone knew. My neighbor then explained to me that the old guy was still alive.
"El vecino explica que él está vivo."