What you saw is called "Dynamic Brake Force Display" or "Adaptive Brake Lights" by BMW and one or two other European automakers: the brake lights' intensity and/or lit area grows in response to urgent braking. More generally, the idea is called "Emergency Stop Signal", and it's standardized in UN Regulation 48 as the stop lamps or hazard flashers blinking rapidly at (3 to 5 flashes per second) under severe braking (may be activated with deceleration equal or greater than 6 m/sec/sec for light vehicles or 4 m/sec/sec for heavy vehicles; must be deactivated below 2.5 m/sec/sec) from speeds above 50 kph/30 mph. This type of system is more widely deployed, not only by European makers but also by Korean, Japanese, and US brands (mostly in markets outside the US).
The difference between the two methods is that brighter/bigger doesn't require specific testing or homologation, as long as the lights don't exceed the permitted maximum intensity for brake lights, whereas flashing does have to be tested and homologated according to the requirements in the regulations.
The similarity between the two methods is there's no data (that I'm aware of) showing an actual crash-avoidance benefit. It's one of those ideas that sounds like common sense, and maybe it helps, or maybe it doesn't, or maybe it makes things worse. Eventually there will probably be data.
One problem with the idea as a whole is that it leads people to tinker with their car's brake lights, most often by adding blink/flash/"pulse" gadgets to the CHMSL (3rd brake light) in the mistaken belief, pushed by vendors of these gadgets, that they'll improve their odds of avoiding a crash.
