@ehdog

In the ER, the focus isn’t on what’s most likely, it’s on what can’t be missed. Even if something sounds like food, hearing black in stool immediately brings up a quick checklist:
Could this be bleeding?
Should we rule it out?

That threshold is intentionally low. Even a small thing gets taken seriously, for a lot of reasons, including keeping the patient reassured.

Online, it’s a different approach. The question becomes: Based on these details, what does this sound like?
And what you described, small amount, mixed with normal stool, crumbly, with a straight edge, doesn’t match how bleeding shows up. That’s why you are being told it's not possible.

The important distinction is this:
The ER wasn’t saying, this is probably blood.
They were saying, let’s make sure it isn’t, mostly for your sake.

Honestly, it’s extremely common in the ER to test stool, even when it already looks unlikely to be blood. It happens all the time. I’ve done it countless times.
And between you and me, it ends up putting money in doctors pockets.