Why does the 830 always point out allies and alternate paths on a previously saved route?

Probably because your friend created a route and not a track. Route have just some points and the device have to calculate the track. 

Ask your friends to export as a track and not a route. Which software he used to create it? 

If you have "turn guidance" enabled (Navigation>Courses>Course Options) it will always take the loaded Course as only your suggestion and it will still plot its own route from your initial starting point and attempting to join up your track points via the routing information in the enabled internal map. Sometimes if it can't find a routing between two of your track points it will re-plot the course to meet up with some further along point. Mostly its route and yours will be the same but not always and especially with bike paths etc.

If you want to follow your exact route then disable the "turn guidance" and follow the magenta course line zoomed in enough so you can se the configuration of junctions.

The issue is that if there are just few points because it is a route he will have some straight lines. 

Thank you. The only thing I see in the manual about "tracks" is "Live Tracking." How do I download or create a "Track?" In Garmin Connect, I only see the option to save as a "Course." Rally, what I'm looking for is turn-by-turn navigation with the exact turns made during a trip. I don't want suggestions, just what the ride creator actually did.

OK. As I mentioned to Simone, above, I just want to be able to save a file that tracks the exact turns I made without suggestions. I can see where turning off turn guidance will eliminate the suggestions altogether but it would be nice to get notifications of an upcoming turn. Especially when one downloads an unknown course, such as when one is about to do a 50 mile ride in an unknown area, it's good to be notified. Otherwise, I guess the alternative is to set the device to maximum zoom and follow the map arrows?

If you create a track directly on Garmin Connect do you have the same issue? 

I guess I'm at a loss here. The only thing I see in the manual regarding "Tracks" is LiveTrack and GroupTrack where multiple people can see each other's position on the map, which, according to the manual, still need a loaded course. If there is a secret track feature, like the secret menu at In and Out, please share.

There are no secret menu items. It is just the naming inconsistency/collision. Both routes and tracks are referred as courses in edge/manual. (see routes vs. tracks at https://support.garmin.com/en-US/?faq=v0rJAHy2hq3prHjRlxdRw5)

There is tracking too. But it is not related to navigation. It is a way you can see where others are (nearby) or allow others to follow your progress during your ride.

Thanks for the link. How do I create and save an "active track log?" And, if I do save it, can it be used for turn-by-turn navigation?

You can select any recorded ride on your Edge unit and convert it into a course to navigate along in the future.  Go to the ride history and select the ride in question to see the options.

You have to have recorded and saved the ride to create a saved course from it.