1) I would assume your entire social network is well documented. A lot of conversations include one person looking something up before or after the conversation. Most conversations don’t come up randomly. That can probably signal that you might be interested in such a topic too.
For 2) it’s worth noting that when you say you didn’t say Alexa, it means Alexa at least thought you did. It’s not trying to constantly record, but may still be a problem to you.
I've been keeping my eye out for good, solid proof that these assistants are doing ad-based targeting based on things being overheard, but I haven't found anything despite looking, and the arguments they aren't are reasonably compelling. (The people looking are quite motivated to find it. Big feather in their hat if they do and can even convincingly cast shade on Amazon, let alone prove it.)
My conclusion is that the targeted ads that people report are either A: coincidence (millions of users, only really tens of thousands of types of "things" to advertise with, sooner or later life coincidences would be expected to happen to large numbers of people) and/or priming (you notice the ad for camping gear since you were just talking about it, but don't notice the several hundred other impressions for camping gear that you just edited out entirely) or B: they didn't get it from your speech; you gave out other signals without realizing it, like a Google search that may not have been "wanna buy camping gear" but unknownst to you is known to be correlated to it, or as you say, your friend ran a search and now you're getting ads, or you're talking about camping gear in the first place because you are in a coffee shop near Camping World Outlet, and in general, the advertising machine knows that you're interested in camping gear right now because that's how well they have you under surveillance... they don't need your actual speech to know that's what you're talking about.
The first is mathematically inevitable, but poorly explains the cases where it recurs to one person. That seems to be the second. In a sort of way, I say that's even creepier than "they're listening to your literal speech and targeting you based on that". They've got you so pegged from everything else they're doing they don't even need that signal. That's creepy.
People have dozens of conversations every day that don’t match with the hundreds of ads they see every day. But then once or twice coincidentally a conversation preceded a relevant ad and the user jumps to the conclusion that their conversation was being listened to without noticing that 99.9% of the time the ads have nothing to do with any topic of conversation. Its occam’s razor or confirmation bias or some other phenomena HN likes to point out.
For 2) it’s worth noting that when you say you didn’t say Alexa, it means Alexa at least thought you did. It’s not trying to constantly record, but may still be a problem to you.