Be very careful. It sounds to me like the VC is considering investing in one of your competitors and they want to use you as 'due diligence' to verify whether there's enough of a market for them to invest in.
If I were you, I'd go into the conversation with the working assumption that everything you say is going to be passed on to your competitors.
It is extremely unlikely they want to fund you. I'd ask at the outset what their motivation for the call is. Ask them to give you their own understanding of the market: how your product compares to others, what they think about the industry, etc..
What they tell you will make it clear if they have looked at your product in more than passing detail. It is more likely that someone has named your firm as a potential competitor in their business plan and they are just doing due diligence as parent-post suggests, in which case they may not even have visited your website.
If they cannot tell you anything interesting about your own product or market then what is the point in talking to them? Politely tell them you'd be pleased to talk when they have a better understanding of the industry and understand what sets you apart. Then get back to coding.
If I were you, I'd go into the conversation with the working assumption that everything you say is going to be passed on to your competitors.