Ethically, do I need to include as coauthor a person who provided basic knowledge to fill a gap in my research?
The International Council of Medical Journal Editors (ICMJE) has established four criteria for being considered an author. The person's contribution should fulfill all four criteria. If not, they need to be considered as a non-author contributor and their contribution acknowledged, such as in Acknowledgements section. You can read about the different criteria and designation here. To directly answer your question, the person would be a non-author contributor.