This is very good question. Suetonius really wrote that Caesar said it. By the way, its position in Suetonius' book indicates that this statement is, according to Suetonius, a blasphemy and thus this idea does not serve to Caesar's honor.
By other hand, Onasander describes in Strategikos the same situation and the same statement, but his story is about Scipio Africanus. Moreover, in some latin editions of Strategikos, there is the note that Suetone (Tranquillis) ascribed this story to Caesar. (My mistake. I've read it, but not in Onasander)
Finally, Sextus Frontinus describes in Strategemata (book I, part XII) both stories. Scipio Africanus said "plaudite milites, Africam oppressi" ("Applaude, soldiers, I'm crushing the Africa") and later, in similar situation, Caesar said "teneo te, terra mater" ("I'm holding you, mother Earth").