A numbers station was a technique used during the Cold War to transmit information in the clear (without encryption) by way of a radio broadcast to agents in the field. An announcer would pronounce a string of numbers, and the field agent would use a codebook, to work out the significance of the message.
This episode is the crossover with Hawaii Five-0 (2010) featuring the Jerry Ortega character played by Jorge Garcia. Henry Ian Cusick was previously in Hawaii Five-0, playing a completely different character than the one he plays in MacGyver
Initially written and filmed with production number 418 for Season 4, but held back due to the pandemic. The original title was "SOS + Hazmat + Frequency + Malihini", so they added another ingredient to the title to match it for Season 5.
In the opening scene, Russ Taylor , pronounced Jerry Ortega last name with a Spanish accent. Henry Ian Cusick, who plays Russ, tends to portray many characters who were born and raised in the British Isles, is actually born in Peru.