Please help me make sense, if the current price of a stock is $100 and someone purchased calls with strike price of $70 in 6 months. How is that possible?

I feel so confused. I'm reading up about calls and I came across this. How does someone purchase calls below the current price? Won't it be expensive? And does it mean they expect the price in 6 months time to be $170? Or they expect it to be $70?