You're correct, but his next post would've been (if he was answering your question) "It's [insert mod name here], its website is [insert website here]!" and it would've been advertising, even though neither of you would have meant for it to be.
I'm not sure how it'll rank up against Doom 3's engine, but I'm too much of a HL fan to give an good unbiased opinion. All I know is if you've got one of the newer ATI video cards, HL2 will run better on your system than Doom 3, and vice versa if you've got a newer Nvidia card and play Doom 3. Both companies backed the two games, and built their cards around each engine.