I don't doubt that if Caesar did say such a thing, that it should be meant as a simple term of endearment or friendship, rather than indications of family biology. I just doubt that someone in those particular circumstances would've had the time or wherewithal to pause and reflect so dramatically. Truly, just reading the accounts (especially that of Nicholaus... thanks for posting that one Cato... which is particularly brutal), it seems absurd that such an utterance would have been made.
As an aside, I am particularly fond of the following Suetonius account:
"And of so many wounds none turned out to be mortal, in the opinion of the physician Antistius, except the second one in the breast."
This is particularly impressive because it is clearly one of the earliest recorded autopsy's in history. What is more significant is perhaps the political implications of the announcement... that despite the assassins attempts to make Caesar's death a deed performed with anonymous unity, this surgeon suggests that only one conspirator was ultimately responsible for striking the blow that mattered. I suppose it is interesting that none of the ancient sources indicate who it might have been that struck that particular blow.
The idea may be ridiculous, because even without that particular wound, it seems likely that Caesar would have bled to death anyway once we consider the nature of ancient surgery and the length of time before Caesar was attended. This obviously does not change the involvement of each particular conspirator, nor their motivations, etc. However, I do wonder if Antistius had any particular political motivation (and if as a result it had any effect on the feelings of the people) or if he were truly attempting an honest medical appraisal.
Sorry for that tangent.