Then why would Thor be so assured that his father is the one who made the decision to set all of this in motion?
Honestly, I still think the simplest answer is that some people are thinking way more about Odin saying "sounds mean" than we're actually supposed to.
Thor says Odin has good days and bad days - the prophecy and what it meant was given on a "good" day, and in the middle of a "bad" day, Odin cant quite remember doing so. Seems fairly straightforward to me.