It is indeed a false positive. Trainers will occasionally trigger antiviruses, no matter where on the internet you get that trainer from. It is because of the way that trainers work - injecting values into your PC’s RAM.
Please use the search feature on the forum, so you can find posts like this one which explains why you are experiencing that and how to resolve it: Windows Defender marked WeMod as a Trojan. 
Since the issue was resolved by @Ptondo, I’ll go ahead and close the thread. Feel free to click the “Solution” button on the bottom of his post, so that the answer will help others in the future.
Thank you and enjoy using WeMod with your games