Depends what you mean by a liar....if you say that he was told that the shutters were forced..but interpreted this as being gemmied...ie paraphrased what he had heard...does this make him a liar.
Exactly. People do not repeat conversations they've had 'word for word' like parrots. We have memories not tape recorders. People tend to convey only the gist of a conversation and use their own words based on their own understanding of what they had been told. Also misunderstandings can arise if the person is not actually at the scene and can only imagine what they have been told happened - with no way of checking whether their interpretation is correct.
It would be a natural reaction IMO on hearing that someone had broken into an apartment via a window to assume there must have been some force involved and to add in that assumption ( of theirs) when speaking to a third party.
IMO It's nonsense to suggest people lied because they may not have repeated 'word for word' the exact conversation they'd had with someone else. Humans don't have the capacity to do that - and we do not have a 'replay' button - only our powers of recall which can vary hugely from person to person.
I don't think Kate, Gerry or any of their friends/family lied about the shutters/windows - they all just said what they THOUGHT must have happened at that time.