The article says he "lived only two blocks away [from 125 St] in Morningside Heights, across the street from Riverside Church", so the author is looking at Harlem from roughly 120 St and Broadway.
From that POV, the boundaries of his presumed-safe neighborhood would be Morningside Park and 125 St.
Having lived within a block or so of the place being described, 125th is a pretty accurate placement of the Harlem's southern border west of Broadway. (Maybe a bit more south at St Clair place.) Further east is different. I can't speak to the situation in the 80s.
I thought about that, but even from the West Side looking East you wouldn't refer to 125th street as the "boundary." I think this is more likely just sloppy editing.
Source: I grew up 15 minutes from there, and lived in South Harlem for years.
From that POV, the boundaries of his presumed-safe neighborhood would be Morningside Park and 125 St.