I know you think you're right about everything, but you're not. LEDs do sometimes go into flickering mode.

Now, show us a link where the emitter is the cause of the flicker, and not the driver.

Oh, it happens; I've had multi-LED panels where handling the PC board (not the power
brick) caused/stopped the flicker. Not solder, either, some kind of internal-to-the-LED
package or thermal fault. Replaced four or five elements, and the lamp works fine now
(though my replacement LEDs were a mismatch for the original 'warm' white).

A lot of the cheap Chinese-made LED bulbs for automotive use seem to
develop flicker problems. One or more series strings of LEDs start
flashing on and off, somewhat randomly, while other strings are
unaffected. These don't have a "driver" per se, just a series
resistor and (in some cases) a bypass cap.

I haven't been able to tell whether the failure is in one of the
individual LEDs in the string, or in the solder bonding of the LED to
the substrate. I sorta suspect the latter... bad RoHS-safe-solder
junctions, perhaps. The flickering seems to be at least partially a
thermal cycling problem... LED comes on, chip heats up, bad junction
opens, LED cools down, lather/rinse/repeat.

The time constant is typically a fraction of a second... more of a
blink than a flicker.