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.
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.
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
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.