Wikipedia points out that, “The Guinness Speed Reading World Record Standards are not known and they have terminated”. Without knowing the standards of the testing, I don’t think it’s possible to use the measurement from 1990 as a fact. I haven’t been able to find any evidence of testing under strict conditions in the 30 years since that one unknown test.
I’m pretty sure that I could read 25,000 words per minute if I printed a single word (like “a”) 25,000 times on some paper, and then flipped through all the pages in one minute. I think more information about the test is needed before coming to any conclusions about it.
Magic tricks are easier than impossible-seeming abilities. Here’s an example: Derren Brown - Library; possible?
There are known cases of people fooling experts with memory techniques, mentalism, or magic tricks, so I think it’s more likely that some kind of trick or technicality was used. 
Photoreading also makes similar claims, but there was a NASA study on Photoreading that concluded that it didn’t work.
Here are some related discussions to check out:
80,000 words per minute is 1,333.34 words per second. I don’t think that it’s possible. Even if someone’s eyes could pick up the words that quickly, I doubt that a brain could process the information.
Does “100% comprehension” mean that all 80,000 words could be repeated back perfectly without errors, or that five basic questions were asked about the content and all five (100%) were answered correctly? More details are needed.
I’m ready to believe it, but I’d have to see very solid evidence. It’s too easy for clever mentalists to manipulate people.
I highly recommend this video, because it goes into some of the ways that people can trick other people into believing extraordinary claims.
Edit: I’m not saying that speedreading doesn’t work. I do think that it’s possible to improve reading speed — but I don’t think it’s possible to read 25,000+ words per minute.