That it was one drawn in the first place, two published having been seen and approved by Guardian editorial staff, three remained on the website for I think about 15 hours in total, and four the anaemic nature of the apology that was issued, containing elements of non-apology (of the 'We are sorry if this cartoon upset some readers' genre).
The isssue of this cartoon, Diane Abbott's recent letter etc is about largely unconscious, anti-Jewish bias by certain sections of those who consider themselves to be generally liberal-left progressives. Rowson himself said that he didn't realise that the cartoon was anti-Semitic until the matter was explicitly brought to his attention, and presumably the Guardian likewise.
Reflects unconscious left of centre anti-Semitism