The moment a conversation is framed as a meeting about your startup, the other person switches into a mode where being encouraging is the polite thing to do.
Keep it small. No deck, no demo, no agenda circulated in advance. You are asking someone about their work, which most people enjoy talking about.
Signs it is going well: they are doing most of the talking, they mention something you did not ask about, they check a date or open a document to get a detail right.
Signs it has gone wrong: you are explaining. If you are explaining, you have stopped learning and started selling — and it is too early to sell.