Call options are generally related to the growth of value of the underlying. Because traditionally a call option would allow you to buy (CALL) the underlying at the pre-agreed strike price, they would be exercised when the value of the underlying was high.
There may be some difficulty to understand the idea of a call option when the underlying is non-tradable - like a block difficulty. You cannot buy or sell a block difficulty but you can still track whether it is falling or rising. If we define a call option on block difficulty then we expect that it is when it is above the strike level.