It's difficult to say for sure without more context (overall attitude of the recruiter, the general geographic area, the job function, etc.) But there are a few likely scenarios.
Most often, a remark like that means they thought your skills and experience might command a higher salary. You should take it as a compliment, but also keep it in the back of your mind when it comes to negotiating your offer should you receive one. You might be able to push to the higher end of the spectrum.
Another possibility is that you're in a location that has a higher than average cost of living. While 40-60 is a great range in Pittsburgh, it would be terrible in San Fransisco. You should do some research into what other entry-level employees make at companies in the area.
Lastly, they may just have been exasperated by candidates before you asking well beyond what they were "worth". In this case it's more of a feeling of relief of finding someone that's reasonably sane in their salary expectations.
As Juha Untinen pointed out, if you're dealing with a contracted or third party recruiter rather than a company employee your willingness to accept a perceived lower pay band affects them directly in the pocketbook and can lead to that type of response.