This is difficult to say. I would be tempted to say it is fine and you can relax but only if this was a minor bleed that has stopped was triggered by something occasional such as some foreign body that was irritating the nose and now has dislodged.
However, because nose bleeds in dogs may be caused by several conditions that require a prompt veterinary visit, I would not say one is not entirely out of the woods until an underlying cause is found.
Therefore, I wouldn't say it is good if a dog's nose stops bleeding, but the dog is bleeding elsewhere because he has ingested rat poison. I also wouldn't say it is good if the nosebleed stops but a tooth root abscess requiring attention triggered it.
Therefore caution is needed, and the safest option would be to see the vet or monitor closely for future nosebleeds or other signs of problems.