Please answer a question about the following article about Multiracial American:

The writer Sherrel W. Stewart's assertion that "most" African Americans have significant Native American heritage, is not supported by genetic researchers who have done extensive population mapping studies. The TV series on African-American ancestry, hosted by the scholar Henry Louis Gates, Jr., had genetics scholars who discussed in detail the variety of ancestries among African Americans. They noted there is popular belief in a high rate of Native American admixture that is not supported by the data that has been collected. (Reference is coming)

Who said many African Americans have NAtive American heritage?
Sherrel W. Stewart
The context states Sherrel W. Stewart, a writer, believes most African Americans have Native American heritage. This is not supported by genetic research done on this topic and the assertion is challenged later in the text. 
Thus, it can be inferred that Sherrel W. Stewart had asserted "that many African Americans have NAtive American heritage"..