If you have an infinite budget, I could 'target' you by purchasing every ad on the internet with the copy "hi bawana, click this link!"

Nearly every impression would be seen by the wrong person, but a few of the impressions would be seen by you.

The rest of the exercise is figuring out how to segment the audience based on whether it's likely/unlikely that you're in the segment. If I know you're from the US and live in California, I can geo-target to that region.

modem ad technology can do it... your mastercard and visa purchase behavior, for example, is available for purchase. That data can be merged with other purchased data, and things like aggregated browsing behavior. This is all done to serve people who may be in my target audience with (semi) personalized ads. The ad may not appeal to you, so it gets classified as spam.

Fairly sure; the ad was literally “hey _____ employees, please hire me!” with a video and everything.

I believe you can filter down to “works at X company” in the ad targeting. It’s possible they did some sort of other broader targeting, though.