Tell HN: Creepy Facebook Ads

Here is the sequence of events:

1. I was talking to a coworker about a brand of shoes.

2. He sent me the link to the website on slack on my desktop.

3. I opened the link on my desktop and visited the site. No facebook activity at all.

I open my facebook app on Phone and bam, I see an ad for the same shoe company.

Is facebook tracking cookies cross site ? Is this possible ? I mean how else they knew. Are they listening to conversations ?