Keeping things short is respectful
In a business setting, I try to avoid answering with anything longer than the initial email (unless the request specifically requires it). I'll endeavour to match the tone and formality, but I consider it much more important to avoid using up someone's work time with unnecessary prose, than to show off my etiquette skills.
I consider the email you describe to be more respectful of your time than one that adds extra flourishes or pads out the text with artificial evidence of enthusiasm, or quoting facts about the company. If it was a quick response, I would recommend assuming that it indicates they are keen to hear more, until you are given reason to think otherwise.
Automated replies
Many people are used to software such as Outlook including automated response buttons, so that the sender can gather statistics on how many people replied with each response. For example, an email may ask a question, and then have buttons for "Yes", "No", "Weekdays only". In that case it would create more work to send a response rather than just pressing a button, as that prevents the automatic collation of results.
As mentioned in OnoSendai's answer, recently Gmail has started including automated response buttons in emails that did not have such buttons added by the sender. Until people get used to this, many people may assume these buttons have been included by the sender, and that it would create more work for the sender to reply with anything else, as would be the case in Outlook. I can't guess how many people will be affected by this, but I have been caught out by it myself, and almost caught out by it further times even after becoming aware of it. If your candidate uses Gmail, they may not realise that a longer email was an acceptable option.