My ex-girlfriend was just very nervous about saying "lie" because it's "bad". So "I'm just going to go lay down on the couch" because "I'm not lying!".
You have probably hit on the real reason for the odd choice of verb 'lain' in the Guardian article - the sexual connotations of the word 'laid' (especially in the context of bodies, and given that the location was in France).
I suspect that 'laid' was changed to 'lain' after the first draft was submitted, possibly following some ribaldry from the copy editor and colleagues.
Which results in amusing scenarios in which people don't realize that e.g. this song is about sex: https://play.google.com/music/preview/Txqbmvyo63hydudrvpj3gf...