Short Answer: Focusing on one technology is better for getting a job. Learning multiple technologies is better for building a career. Decide which of the two is what you want, and go from there.
Long Answer: Learning multiple technologies will make you a better software developer. No question. If you only focus on one thing, you'll be great at that one thing. You'll also only get experience in one technology (and the necessary support and tool stacks), and probably pigeon-hole yourself into a single knowledge domain as well, and eventually that one thing you choose to focus on (very early in your career, I should note) will be all you can do. It's hard to get out of that position professionally, as everyone who sees your resume will only see that you've been doing the same thing for years, and it doesn't show that you're able to learn or that you're willing to try something new.
That said, specializing and focusing on one thing can be good if you want to get a job, as you'll be very skilled and knowledgeable in a specific area of technology. You can become successful as a specialist, but you live or die by the popularity and lifespan of the technology you picked.
It's also a matter of taste. Whoever was interviewing you has a very short-sighted idea of what knowledge and skill are composed of, and is an idiot. Or, they saw that you are new and thought they could make you feel like you were barely qualified for the position, so that they could make an argument against paying you fairly, in which case they are shady and I wouldn't trust them, and certainly not accept a job from them.