For example, if I state "I had chicken for lunch" and you reply "I find that hard to believe.", I think the implication is clear that you think I'm lying. Alternatively, if a third party says "kbenson had chicken for lunch" and you say "I find that hard to believe", there is not a clear implication that the third party is lying, nor that where they got the information from is lying, as there are multiple locations in the chain of authenticity of such a statement where a mistake or purposeful misrepresentation could have happened, so it's not clear where fault may lay.

So, when someone states "I don't use any of the default iPhone apps" and another person replies directly to them with "I find that hard to believe", I think the implication that they are lying is clear (whether or not they were actually lying).

Now, as for your specific assertion, I think you are obviously correct in the general sense. Although am interested in your opinion on how you would classify someone that is very loose with regard to their statements and their certainty regarding those statements. If I made a statement asserting something, but thought there might be a 15% chance I was wrong if I really looked into it, would I be lying if I stated it as a fact due to the false certainty implied?

Specifically, in this case, if the author was 85% certain they didn't use any default Apple apps and stated as much without qualifying with "I think", or "probably", they may believe they are correct, but be ultimately wrong. Was it a lie to imply a higher level of certainty than existed? I'm not entirely sure how I would classify that. (Note: I don't mean to imply a specific state of mind for the original commenter, this is purely a thought experiment and that statement was handy).