They're probably thinking of Grant Imahara and/or Jessi Combs who died in 2020 and 2019 respectively. They were both on the show for periods of time but not quite as well known as Jamie and Adam
From Wikipedia:
Combs died on August 27, 2019, after crashing a jet-powered car while setting a land-speed record as part of the North American Eagle Project on a dry lake bed in the Alvord Desert, Oregon.[2][3][7][8] The crash was caused by a failure of a front wheel, likely caused by hitting an object in the desert, which caused the front wheel assembly to collapse at a speed nearing 523 mph (842 km/h).[25]
Imahara died on July 13, 2020, at the age of 49, after suffering a ruptured, previously undiagnosed, intracranial aneurysm.[37][3]
They’re often undiagnosed because they can develop over time and regular MRIs and CTs without a reason aren’t really a thing because they’re expensive.
One day you could just bump your head, go for a jog, or even sneeze and then boom, dead.