I am not personally familiar with that kind of software. If I were to know for a fact (or with reasonably high amount of certainty) that his claims were false and/or misleading then yes I would say negative, or at least a neutral would probably be appropriate. If you (or someone you trust) thinks that his statement is at the least misleading then I think a negative is more appropriate.
There is really not anyone that has posted in that thread that I really trust, so I cannot say one way or another that his statements are misleading, and the "tie" should go to the person who you are considering to leave negative trust to. I also know that people with antivirus have had their bitcoin stolen/hacked when their private keys were on a computer with antivirus software, so at least in theory what he is saying is true.
I would personally say that a stronger argument to leave him negative trust would be if he were to say that he was actively trying to hack other people in efforts to steal their money. This is also generally what the primary reason why the OP left negative trust to that person, and I was primarily responding to the rating that the OP left.
edit: I think if some additional information is researched then a negative rating would probably be more appropriate. If someone were to really care, then maybe they could ask the OP to upload a copy of the program to
virus total, and if the file he uploads shows any warnings, or if he is unable to upload a file that does not show any warnings then a negative rating would probably be more appropriate.
edit2: posted in his thread