Either he's saying dice are stoneage tech and thus silly or that you can still fuckup entropy generation if you don't know what you're doing. For the latter, you can do this by having insufficient rolls. Since each six sided die has log2(6) = 2.58 bits of entropy, to get 128 bits you need to roll 50 times (128/2.58 = 49.61) and then pass the roll data (e.g., "623415325...") into a crytographic hash function with at least 128 bit output (e.g. SHA256). If you don't use a hash because of modulo bias, the entropy per roll is only 1.67 bits so you need 77 rolls. Some people might even just roll 10 times or whatever and think it's secure. Point is, you still can fuck it up.