Steve Jobs once announced that iTunes’ much used shuffle feature would be made less random as true randomness often clustered, by chance, into consistency.

If a bitcoin mnemonic phrase is seeded from a very random (high entropy) source it should be safe however it could, by chance, result in a very low entropy phrase like a grammatically accurate sentence or a pattern (bacon cheese bacon cheese bacon cheese bacon cheese bacon cheese bacon cheese), etc. There are many automatons loaded with such seeds, continuously scanning new blocks to find coins locked to keys derived from such seed phrases. They assume people will make their own, more easily memorised phrases and send coins to them.

So, if a randomly generated phrase looks a bit too human, perhaps generate another.

(The chance of this happening is very low).