Was this real traffic though? Google Analytics had a massive spam referral problem in 2014, maybe earlier as well [0]
"The problem of fake references in Google Analytics has changed significantly over the past few years. In 2014, we had some bots from semalt and buttons-for-website that visited your website and left fake referrals in your analytics. In December 2014, the attacks began taking advantage of a weakness in Google’s new Measurement Protocol that allowed direct attacks on the Google Analytics tracking servers without having to actually visit your website. This is a lot easier than crawling the web looking for new websites. "
"The problem of fake references in Google Analytics has changed significantly over the past few years. In 2014, we had some bots from semalt and buttons-for-website that visited your website and left fake referrals in your analytics. In December 2014, the attacks began taking advantage of a weakness in Google’s new Measurement Protocol that allowed direct attacks on the Google Analytics tracking servers without having to actually visit your website. This is a lot easier than crawling the web looking for new websites. "
[0]: https://help.analyticsedge.com/article/definitive-guide-to-r...