Accidental ingestion of 1 strand of hair will not cause much problems.
You might see the rest of the broken hair in the next poop too. Or he might have ingested just that length of hair only.
Don`t worry. But be sure that the floor, play area, toys etc are clean so that such an incident does not happen again. Since hair is not digested by our intestines, if ingested in large amounts, it will be a problem.
Till Your baby stops mouthing all stuff, you have to be very cautious.
All the best. Happy parenting