WhatsApp web on chrome for android

Well, I’ve opened my boyfriend’s WhatsApp on my phone (chrome for android) and the thing is, when I close the tab it keeps online for like 10 minutes. I’ve ran out of ideas to try and disconnect it quickly, I tried closing the page, going forward, going backwards, reloading, turning down the internet for a few minutes. Any more ideas?

Ps. I’m not looking for moral advice, only ideas to turn the app offline, thanks.