Two things to note:
Firstly, both searches demonstrate a nice positive upward trend in articles mentioning the respective search terms. Secondly, the charts clearly show that the trend in mentions of 'Engagement' predates the trend in 'Social Media' by almost a decade.
(N.B. The search for "engagement" is actually the aggregated search on over 60 bigrams like "engaging audiences", "emotional engagement" and "engages with")