Easy, the reason is that earnings are due pre-market tomorrow.
The GREATEST percent yield on an option that goes up or down happens the closest month toards expiration. A May 40 call moving higher will appreciate faster than a September 40 call with the same increase in stock price due to being closer in expiration.
In fact, if there were to have been an April 40 call expiring THIS Friday, it would have been the better buy yesterday, because the percentage increase in price would be much higher than a May 40 given the same increase in stock price.