Does your friend use social media apps on their, like Facebook or Instagram? Assuming they also have YouTube logged in on that device, it's not impossible that an app may have picked up a conversation and this resulted in a targeted recommendation.
https://support.google.com/youtube/answer/6342839?hl=en&co=GENIE.Platform%3DDesktop
https://dma.org.uk/article/is-facebook-listening-in-to-my-conversations

