Venting, venting, only venting but arrrrrgh!
Contrary to your base assumption, I am not a moron.
When I use mixed metaphors -- and you may note I only do it in the first person section -- I am using them as a form of characterisation. The same applies to the odd word choice. Yes, you are correct, "tiny" would be a more sensible word to use of a grain, even a metaphorical "grain of truth" than "distant". I used "distant" for a very specific reason. This is first person. First person works that way. Every word in first is a word the character has chosen and which conveys that character's thoughts. In a way, you can think of it as being all dialogue. If you had your way, you would bland everything worth having in this voice out of existence.
Furthermore, if I had wanted to explain terms before using them, I would have. I explain them when I want to explain them, I am aware that use of them before explanation is to unenlightened readers. This is a thing we do in SF. Don't worry about it. My test mundanes had no problem with it.
In addition, I do not use British spellings out of some strange desire for authenticity and anachronism, I use them because I grew up in Britain and they seem natural to me. In general, I'm quite happy for you to change them to US spellings. For this particular novel, which is the most English thing I've ever written with the possible exception of the story about pulling wings off fairies, I think there is actually a case to be made for using "aeroplane". I can live with "airplane", but I definitely want to keep "hoarding" rather than "billboard". That isn't in fact spelling. Really, not only am I not a moron, I'm not expecting this to be read by morons. If the US reader doesn't know what a newspaper hoarding is, they'll figure it out from context or remain confused. Telling them it's a billboard won't help. It isn't a billboard.
The real problem I have with you is that I don't trust you. I think that's your problem with me too, essentially we need an atmosphere of mutual trust, and we don't have one. I know I don't use enough punctuation. This is an area where I really like to let the copyeditor help. However, if every one of your word corrections is wrong, how can I trust your extensive use of commas and semi-colons above mine? This means that every single comma change causes me distress and anguish. Thank goodness you didn't get to do Tooth and Claw.
Now the good news. Astonishingly, for a copyeditor, you seem not to mind "towards". This is clearly a case of evidence that nothing is perfect, not even things that appear to be perfectly awful.