Its explicitly stated on the website NOT to use any kind of computer generated password. You should, as the author intended, use a physical dice, write it on paper, and then shred, molch and burn the paper afterwards.
You should only use dice ware for your master password or a password you need to remember in your mind. Everything else is auto filled, so should be 20+ random character's of upper and lower case letters, numbers and special characters.
Diceware is intended for memorable passwords, but it is not needed if you have a password manager. Password manager 20 character passwords are cryptographically more secure than a diceword password of similar length due to character set. You have a 100+ character set to the power of 20 which is a lot more possibilities than 4 words from a fee thousand. They are both secure but random passwords should be used for anything you don't need to remember.