EDIT: but as wcoenen points out, this was written in 2009 and Java 1.7 does a better job with some of this.
Yes. I like how you qualify the statement. Furthermore, on the C side you have Linus and other C gurus that really, really know how to exploit the strengths of the C language.
(1) Blind faith in Generics.
This alone screams newb to me. He says that he got better performance with a custom data structure (no shit sherlock) but then seems deeply surprised by this. Duh. Okay, well, obviously he's relatively new to Java, but hey, he could still be a performance expert.
(2) Never mentions the biggest weapon in the C vs Java arsenal. The thing is that C is only able to make optimisations up to a certain point, but there are optimisations that can only be made at run time not at compile time. So Java starts off behind, but can catch up some or even all of that distance.
People have used this to demonstrate Java code running faster than C code, but that is old news, a newb might not know this.
(3) Does not mention the second biggest weapon in Java's arsenal in the Java vs C speed argument. That being that more recent versions of garbage collection allow for super fast memory allocation - enormously much faster than what you get with malloc.
(4) Never quantifies how much slower Java is. If Java is 5 or 10% slower, then Meh, is that really news? If Java is 2x slower than carefully hand-tuned C by guys with actual code writing credentials like Linus, then that is still pretty good. 2x screamingly fast is still more than good enough for most people. If the difference is an order of magnitude, then that is not so good. If the difference is two orders of magnitude, then you might as well be using some scripting language.
A proper expert would certainly have quantified the speed difference.
In theory, any VM language will be slower than a memory managed app.
Then again, the dragon book is hard :)
In case if you are the expert, I would assume that he wouldn't mind if you have any insights to tune in the performance of JGit even further. You can start by joining in the mailing list.
He wasn't quantifying anything since he was not answering your question, he was sharing his experience.