Time Machine when backing up from a Mac to a locally connected hard disk allows you to chose whether to encrypt that hard disk or not. Most people would not need to encrypt it.
It is possible the drive in this case is despite what you are currently thinking not encrypted, it will however be formatted as a Mac compatible hard disk and not as a Windows compatible hard disk. This means it will likely be partitioned using the GUID scheme rather than the Master Boot Record scheme, and also that the partition/volume will be in HFS+ format and not FAT32 or NTFS.
No while it is certainly true you are not going to be able to read an encrypted Mac disk on the Windows PC, it is possible to read a Mac formatted but non-encrypted disk on Windows. To do this will however require installing additional software for Windows to let it understand HFS+ format partitions.
There are several utilities available to let Windows read (unencrypted) HFS+ volumes, below are some of them.
http://www.mediafour.com/products/macdrive
http://www.paragon-software.com/home/hfs-windows/download.html
free version of above for Windows8/8.1 http://www.paragon-software.com/home/hfs-windows-free/
Note: If a Mac backs up to a network Time Machine server instead of a local hard disk then it will always be encrypted, however your friend is unlikely to have used a server to do this so it would not apply. However if you have used a Time Capsule made by Apple then this is a WiFi router with a built-in network Time Machine server and this would be encrypted. I still suspect this does not apply either.
Finally, assuming you are able to connect it to the PC and using a tool like those listed above read it Windows itself will not have a Time Machine client to navigate the backups, you will therefore have to do the handwork yourself. This should be possible though, you would navigate to the relevant folder and copy from it to your Windows drive. DO NOT try doing a file-search, I cannot see Windows being able to cope with searching all the links Time Machine uses.