Some of PewDiePie's more avid fans have taken to hacking to convince people to subscribe to Kjellberg, whereas others, such as well-known YouTuber Mr. Beast, have chosen to buy virtually every advertising spot in their home cities (including billboards) to get the word out.
It's worth noting that the hackers' true motivations between both of these attacks (they seem to have been perpetrated by the same individuals) could be more legitimate than they appear. Though the printer incident involved fairly straightforward "Subscribe to PewDiePie" sentiments, this recent Chromecast attack appears to be more of a public service announcement.
"YOUR (sic) Chromecast/Smart TV is exposed to the public internet and is exposing sensitive information about you," the video allegedly being displayed across Chromecast-connected devices claims. While we can't confirm that statement ourselves, the fact that hackers have been able to access users' Chromecasts does seem to imply that some sort of vulnerability exists.
With that in mind, the hackers in question could almost be considered security researchers; albeit ones with vigilante leanings. They're finding vulnerabilities and exposing them to the world, which will likely force device developers to patch the issues more quickly.
Chromecast community managers have reached out to affected users on Reddit to gather information and pinpoint the cause of this latest round of device hijackings - we'll update you if they disclose the source of the problem or announce a fix.