I'd go with grain or more likely flour/unmixed dough
It's very unlikely to be mould in between slices like that, even if pre-sliced, and essentially impossible if you just cut it.
Bread is also generally made and shipped pretty quickly, so if it's got a few days left on its date (or was bought loose, meaning it should have been freshly baked) it shouldn't have had time for mould to form.
As you say, it doesn't look (or feel) like any of the mould found on bread, which is usually fluffy, hairy, or even scaly. It does look like inclusions I've sometimes seen on home made bread when barely cooled enough to cut - no chance for mould.
So I'd eat it without worrying. It does look a little like a grain, but if I see that in my home made bread, it's flour that's got wet but not mixed in properly (often near the top as it was stuck to the pan while the loaf was rising).