This is true, but I'd add a caution: just because something seems outlandish or improbable doesn't mean it actually has a low prior probability. Human intuition on what's weird and what's not is not a reliable oracle of prior probability. If you're going to give the prior an actual number, you better base it on actual facts.
In your example, based on existing data, it is indeed fair - some dogs do sometimes eat homework, whereas there are no verified accounts of aliens stealing it. So that's a legitimate adjustment of priors. Particularly if you actually have data on the incidence of paper-hungry dogs.
But in science and philosophy, there's lots of important questions for which we can't legitimately calculate priors, and "it would be too weird" is not at all relevant when determining their values.
But we do have reasonable priors on parapsychology from its wasteland of unreplicated, flawed studies, with no convincing results despite decades of effort.
In your example, based on existing data, it is indeed fair - some dogs do sometimes eat homework, whereas there are no verified accounts of aliens stealing it. So that's a legitimate adjustment of priors. Particularly if you actually have data on the incidence of paper-hungry dogs.
But in science and philosophy, there's lots of important questions for which we can't legitimately calculate priors, and "it would be too weird" is not at all relevant when determining their values.