A calendar spread involves buying and selling two options of the same type with the same strike price but with different expiration dates. Risk reversal, on the other hand, is an options strategy that combines buying and selling calls and puts to reduce risk. The fact that both of these sophisticated investment strategies are being used indicates that experienced and knowledgeable investors are getting involved.
The unidentified whale behind these trades has seemingly taken advantage of the lower implied volatility for the monthly delivery period. In options trading, IV is a measure of the market's expected volatility of a security's price. A lower IV usually indicates a lower expected volatility, suggesting a more stable price.