Simple explanation: they did in fact see what you were doing and just didn't want to tell you because they don't want to teach cheaters how to evade bans. They were hoping after the first review that you would start playing by the rules.
I'd also further assert, that simply being an HN reader means you are more likely to trigger a false positive than the rest of the population. Blizzard does some very aggressive memory scans, and they look for tools that are much more common with developers than the rest of the population. I've personally used a well known library for code injection, that if I'd had it running on an unrelated binary while playing WoW they would have seen the signature of the library, and likely Blizzard would have eventually banned my account.
I don't know if the parent was doing things that Blizzard considers naughty or not, but I'm willing to give them the benefit of the doubt given what I've read about Blizzard's Warden.
Some cursory research told me that new accounts with a lot of market activity were a "red flag" for the automated system due to similarity with bots that created new accounts to evade bans, which I guess makes sense. Of course this is the internet and you have no particular reason to believe I was or wasn't cheating on World of Warcraft, but for what it's worth this HN account is linked to my real identity and if I were cheating all the time I would know better than to brag about it or even obliquely reference it in my posting here.
Yours is simply the latest in a line of those who have followed the letter of their Auction House rules, but not the nebulous and unwritten "spirit".