You are certainly entitled to your opinion. I have not read anywhere in MSM or from Alex's family that he jumped off a bridge. The only thing that has been reported is that he was found on a riverbank. If LE was staging off the bike trail near the river, its entirely possible that both facts are true. LE does not always stage exactly where a body is found. They need to park vehicles and search for evidence. They may have been looking for evidence where you saw the lights after 5pm - 2 hours after the body was found. If Alex did not have all of his belongings with him they may have expanded the search area to try to find his phone or keys or whatever. Crime scenes can cover large areas.
I don't really see who would benefit from changing the story from he was found in shrubbery to he was found on the river bank (in shrubbery). I guess I'm just not seeing the reason or need for anyone to secretly change a location. When there's no reason for doing something, the simplest explanation is usually the answer - original reporting reported exactly what reporters saw with their own two eyes and changed as LE/the family released more information about the exact location of the body.