The title of the thread is incorrect. The report from CSNNE, that the video is quoting, says "frontcourt" not specifically "big man". A SF is part of the frontcourt, so this also could include players such as Hayward, George, and Butler.
The actual statement in the video
"According to CSNNE multiple league sources have them in recent weeks that the Celtics are focused on landing an all-star caliber talent in them in the frontcourt"