I didn't draw this conclusion at all. From the actual article it states initially the drives weren't encrypted at all so the flash dump lead to completely accessible contents. Now the flash dump is encrypted but the key is in flash memory which is simply locked by a pin. Even with a fully AES encrypted drive, you can brute force that with the standard 4 digit pin in 15 minutes. The hard part is not working out the AES key the hard part is brute forcing the pin sitting in the front which leads to the AES key sitting in standard flash memory. Yes a longer pin takes longer (55 days for the 8 digit pin) but one can imagine emulating the entire flash dumped iphone in software and parallelizing that just to pull out the key from bruteforcing the pin..