Headscratchers / Scooby-Doo and the Alien Invaders

• After the Mystery Machine broke down and Daphne suggested that the spaceship was a jet, Fred replies with “Not like any jet I’VE ever seen.” However, the next morning at Sergio’s Diner, when Daphne brings it up, Fred says “It must be a new kind of JET or something.” What made him go from one opinion to the other? Did he sleep on the matter?
  • Technically speaking, Fred said it wasn't like any jet "I've ever seen" with an unspoken "before" at the end, this it would not dismiss the idea of the UFO being some new model of jet.
• Why were Laura, Matt and Steve so excited about the aliens being real, as well as the kids and Scooby-Doo? After all, if this is in the same continuity as the original series, then they'd already know about Superman, The Martian Manhunter, etc., ESPECIALLY since they'd teamed up with Batman and Robin twice.
  • What do you mean by "original series"? "Scooby-Doo, Where Are You?" had two seasons and no guest stars. There was "The New Scooby-Doo Movies", which did have guest stars each episode and which featured Batman in two different episodes...but this isn't part of the original series and so might very well not be canonical within the Mook DLE direct-to-video Scooby-Doo films.