The way torrents download is in chunks which are not necessarily, if ever, representative of the component files. It is therefore necessary to download some parts from other files before the download you want can be completed. It is likely that the two "other" files you have are not complete.
You may be wondering what will now happen to those segments and I am not sure to be honest and have a feeling the behaviour of Frostwire concerning them is different in Frostwire 5.0.9 which I am currently testing, and as yet is not ready to let lose on the public. In a few days it will be.
I hope this helps.
Please do not Private Message me with questions that can equally well be posted in the forums, and may also help others. Do use the forum search.