The dictionary definition is: a widespread occurrence of an infectious disease in a community at a particular time.
"Infectious disease" being the key. If we limit the definition to "took off" then any new and popular software becomes an epidemic.
It's naive to assume that something like this couldn't possibly be politicized simply because it relates to health. His points absolutely could be relevant to how the Surgeon General chooses to describe the uptick in vaping.
Overall tobacco usage is still going down: https://www.cdc.gov/tobacco/data_statistics/fact_sheets/yout...