I can't imagine that he said 4 words are enough for a BTC mnemonic.
Using the 2048 word BIP 39 list, each word represents 11 bits of entropy
Thus, 4 words = 44 bits of entropy.

44 bits of entropy can be brute-forced in a matter of months, even at a reasonable 1 million guesses/second.


At a minimum, if you consider your adversary to have an NSA-level (according to Snowden) 1 trillion guesses/second capablilty
you would need at least 7 words (77 bits of entropy) to make brute-forcing your mnemonic unlikely for at least your lifetime.