It’s difficult to know for sure without the full context, but I would be wary about this. I would confirm the VC’s interest in you as a standalone investment first. Ask them -- I’m happy to meet the portfolio company, but just for our process, how compelling on a scale of 0-10 is our startup to you as an independent investment?
If you don’t get a 9 or 10, it very well may be that the VC wants to see if his portfolio company can do what you are doing (and may want them to learn from you) OR he may want them to acquire you. Synergy can be code for acquiring you, basically. And you should in general avoid this. Mergers of startups are huge time wastes and time sucks. It’s better for you to go get funded yourself.
I say this because in general, VC’s don’t make multiple investments in the same space. They usually are hunting for big unicorns that will be billion dollar plus markets. And there’s usually not room for 2 investments in the same space.
So it’s more likely they want the portfolio company to learn what you’re doing and adapt / acquire you. I would try to get an honest answer from the VC before you engage on their intention.
During the meeting -- if you do have it -- I would treat it as much as an opportunity for you to learn from them as they are from you. That is, I would try to set the agenda upfront where you say you have a deck and can share some details but you’d first like to ask them questions. Get their consent on this. Then spend ideally 20 minutes of a 30 min meeting understanding their strategy / positioning / issues, etc. And then when you share, decide how much detail. I think it’s best to stay very high level and explain you are still wrestling with figuring things out if you get the sense the VC’s not serious about investing.