This isn't a Guinness World Record. Let's make that clear from the off. For that 30 Hennessey Venoms would need to be built to qualify it as a production car (oddly, only 29 are to be made), a two-way average would be needed and a Guinness official has to be present. See Hennessey's comment for full clarification.
Instead, this video is just a phenomenal display of speed. The recorded terminal velocity of 270.49mph amazingly isn't the most startling part, it's the ridiculous acceleration. From 100mph to 250mph, the Venom is just relentless; it appears the video has stopped with the gearchange pauses such is the ferocity with which it piles on speed. Even the final 20mph is accrued pretty swiftly.
There's plenty of patriotic flag-waving (literally and figuratively!) for America in Hennessey's video, but that shouldn't detract from a stunning achievement. When can we drive one?