Again, I hate to be annoying, but it comes down to the probabilities involved. (That is why I waited for ThePhy to answer the tennis ball question)
As I said, I am guessing that SETI is looking at EM waves. I'm too lazy to Google it, and it is irrelevant anyways. But what is relevant is the actual probability of the signal received in the amount if data examined. How do the electromagentic waves correspond to the letters in the message you posted? What types of patterns are they looking for? Is it encoded in ascii?
So, we are disregarding a hoax, and I assume we are disregarding the whole issue of the fact that the message is in English...or are we? That is what is unclear.
If we assume that the signal stream is all lower case letters, commas, spaces, and periods, we sill still have enough characters to generate Knight's hypothetical message. His message is 211 characters, with 29 possibilities for each position, so I'd say it is pretty unlikely. :chuckle: A random string of 211 characters from the character set would have a one in 29^211 chance of being Knight's message.
There you have it, or at least pretty close. The messages in a continuous stream of characters could be any length, not just 211, so I think the probability of a similar message randomly occuring would be higher. I'll agree to ignore that.
So, if they only looked at 10,000 characters, and their equipment was not faulty, there was not a hoax, etc., and my only two choices were random event or signal from aliens, I'd go with the aliens. If they looked at 29^1000 characters, I'd be surprised if they didn't find Knight's message.