If he had hard sex or even bent his penis in a slight way during intercourse it's possibly he ruptured a small blood vessel.
You also state he's had frequent bowel movement has there been any blood in the stool? If he has increased any fiber or fruit lately that would explain the frequent bowel movements which could also cause bloating. At this point though I would say those two are not related to the blood in the penis.
If this is the first time and there has not been anymore blood coming out, I feel that some how during the sex last time he may have ruptured a small vessel.
Now it is also possible to have an infection which may or may not have other signs at this moment. Only way to know that for sure it to have a swab test from a doctor.
At this point, if he's feeling fine, ie; no fever, no pain upon urination, no lack of urination and of course no more blood spots, I wouldn't worry about it too much. If it does appear again, or any of the others above begin to happen, I would have him checked out.
Stress can put a huge strain our systems too, which could be a cause for the frequent use of the restroom and bloating. Which can give each person different results.
So at this point monitor it see how he does. Let him or hopefully he will just relax for today and not worry or stress over anything.
As far as the blood on the underwear, not much they can do with that at this point. If he needed to they could do a swab collection from his penis if it came to needing a sample.
Hope this helps, If you need anything else please feel free to ask. If you found this helpful don’t forget to click the *accept* button!
Just to add since it's not 100% if there was some blood in his sperm:
Blood in the semen may be caused by inflammation, infection, blockage, or injury anywhere along the male reproductive tract. Could indicate disease or a problem within the urethra, testicles, epididymis, or prostate.
It is usually the result of inflammation of the seminal vesicles, and will usually go away spontaneously. Often, the cause can not be determined.
Hope this helps too!
Honestly without seeing your husband in person, it would be hard to say. It is possible that it had clotted inside and then it just came out. You only mention the one spot. If there are more spots or was continue bleeding then I would be concerned. But with no other problems such as burning, pain, lumps.. it doesn't appear as it may be anything to worry about. Now it doesn't mean he may not end up having some of those other symptoms. If he does then I would get him in to be checked.
Just say it was part of his sperm, then a portion didn't fully come out with the ejaculation, then we are back to my last post of it usually may be the result of inflammation of the seminal vesicles, and will usually go away spontaneously.
So at this point, monitor and keep an eye on what may be going on.
Hope this helps.