It’s almost certainly not a virus. It happens fairly often with Garmin downloads, partially because if you have enough “random” data it’ll eventually it’ll trigger an AV pattern-match, and Garmin downloads are quite large.
The “won’t open” problem is likely your AV stopping you accessing the file.
Without knowing exactly what you downloaded and what antivirus has the problem on what version of Windows (and what virus it thinks it has found) it’s a bit difficult to say more.
