There have been a few people who saw the same thing on the Lightning, indicating it may have 400+ mile real world range but I did see one counter point to that which seemed very reasonable. If they had just ported the Mach-E interface to the demo Lightnings then it may be confused about the range capability due to a much larger battery. I can understand if Ford sandbagged a little on the predicted range, like saying their target was 300 and the actual EPA range was 310 or 320 but sandbagging 25% doesn't make sense.
I have a day 1 reservation for the Lightning so I can get one of the first trucks off the line but I would jump over to a Rivian if the price was right and I thought I could get it in a reasonable amount of time. As of now I don't think I'd get a Lightning until middle of next year, at the earliest. Definitely could be end of year or later depending on production ramp up. I don't know what kind of order backlog the Rivian has. Looks like they are asking for $1000 for a pre-order so the line probably has less fence-sitters than the F150 line.
ford has sandbagged their HP ratings on the mustangs as well so it's not unprecedented for them to do similar. for instance, they claimed the gt350 made 526hp but real world dyno's (many different ones) have them making more like 580-590hp.