Apparently, it was for some. I think it was more so due to "black" meant "dark" to many -- and we had colorism issues -- and dark sadly meant ugly to many -- and we see that is still a issue for many today.
African-American --was used by white yes -- because they knew our origin -- as we did -- but we still knew we were Black/Negro first. I haven't seen in any narratives or studies where Blacks called themselves "African-American" in large numbers or as a description before Jesse.
I used to be ok with African-American - but I prefer Black - and I have only ever heard my family say they were Black - not African-American unless that is the only thing to pick.
On Black Power:
Black Power was popularized by Stokely but not coined -- he was given permission and push to use by the person who coined it -- Willie Ricks.
In fact, “Black Power” had been used as a civil rights rallying phrase by Willie Ricks, an SNCC man, before Carmichael used it on the “March Against Fear”. Ricks was so pleased with the response to the phrase that he urged Carmichael to use it in his speeches. However, not even Ricks could have predicted the response of the crowd to the phrase. Each time Carmichael shouted out “What do we want ?”, the reply “Black Power” got louder and louder. After June 1966, the call also was used by militants in anti-white rhetoric.