Hi there and thanks for your question.
Blood certainly can be present in a dog's stool because of stress. When we see blood in the stool it usually means that there is inflammation in the colon. For some reason it is quite easy for dogs and cats to bleed from their colon compared to people. Inflammation in the colon can be caused by a dietary change (either a new food or a new treat or garbage), or by stress.
As long as your boy is feeling well and eating well I wouldn't be too concerned. The blood should be gone within 24-48 hours. If this progresses to diarrhea with blood, he may need a 24 hour period of fasting followed by some bland meals of chicken and rice.
If the blood persists for more than a few days or if he seems to be not feeling well or not eating, then a vet visit is in order.
I hope all is well!
I hope this information helps! I will be online for a short while more. So, if you have more concerns about this question you can just hit reply. However, my baby will be waking up from her nap soon and I will be offline after that. If that happens I will respond when I come online again.
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would highly advise contacting your regular veterinarian.