I think there are two separate things. Walking, jogging, riding a bike through a cemetery doesn't seem inherently rude, but to some extent it might depend on the cemetery. For example, Mt. Auburn near Boston was designed for people to use as a park in addition to being a burial ground, so I don't see any reason why it would be rude to do so. There are likely others where that is not allowed.
I think the primary purpose has to be burial and the services around that, so mourners, whether part of a service in progress or sitting by a grave, take precedence and every effort should be made not to disturb them. So if one is jogging or having a picnic or reading a book, you should avoid disrupting mourners and also move if you realize you are in a place where someone who wants to visit a grave needs to be.
Yes, but also bearing in mind that someone who is walking, or having a picnic, or reading a book may in fact *also* be visiting a grave, and may need to be there. I have a close friend whose brother died in his early teens. She has told me that when the weather was suitable, she would often go and sit by his grave while she did homework, that she took her first boyfriend there and sat down with drinks and snacks, because that was something she felt she needed to do to grieve for him, and feel he wasn't forgotten. If you didn't know that background, you might assume she was just using the graveyard as a quite place to read, or study, or picnic. Of couse you should avoid disrupting funeral services.