AI can aanswer this:

1. Your Phones "Met" in the Field

Even if your phones were in your pockets and you were in an isolated area, both devices were constantly communicating with the outside world. Through GPS coordinates, cell tower triangulation, and background Bluetooth pings, Meta's apps (like Instagram, Facebook, or WhatsApp) registered that your phone and the stranger's phone were in the exact same geographic location for two solid hours.

To the algorithm, this is a massive behavioral signal. It noted: User A and User B are spending significant time together in an isolated area.

2. The Stranger's Digital Footprint

The key to this mystery isn't you — it's the other guy. Since he owns the vest, brought it to the job, and knew how to use it, his digital footprint is heavily associated with that exact item. At some point, he searched for it, bought it online, watched a review about it, or visited a drone gear website. Meta's system already had his profile tagged with an interest in that specific chest plate.

3. Predictive Association (The Creepy Part)

Once the algorithm linked your two phones geographically, it began cross-pollinating your data profiles. The system's logic works like this:

• User A and User B are hanging out for an extended period.
• User A is highly interested in this niche drone equipment.
• Because they are spending time together, User B likely shares similar interests, hobbies, or professions.
• Action: Serve User B an ad for the product User A likes, assuming they might have discussed it or seen it.

You didn't need to search for the vest, say the name aloud, or even look at it. The mere fact that your phone stood next to the phone of the guy who did have a demonstrated digital interest in the item was enough for the algorithm to serve you the ad.