I am still new regarding privacy and all that, so i am sorry for any mistakes/ newbie questions.

I and my friends were talking on Discord regarding the Oxenfree plot (a game about a time loop). One of the plot points mentions a submarine. To his surprise, He received a youtube recommendation about a nuclear-powered submarine as shown:

he was a bit spooked about this and asked if Google is listening. I asked about his browser and extensions, to which he answered that he's using google chrome and the extensions below:

my question is: how did this happen, and what should he do next to avoid this happening again?

thank you in advance.