Yes, someone with more experience, can go from all those adventures, to settling down with just one/two/handful of people.
In poly, it is quite common, that people start out with a stage of exploration. They might first try swinging, or a open marriage. Maybe it doesn`t feel good, maybe it feels like something is missing. So they keep working at themselves, trying to figure out who they are, and what they need.
Many, find poly, and poly partners, and have that feeling of wanting to settle. It is a very natural feeling. It gives some people that sense of 'coming home'.
Same can happen in a monogamous relationship. Someone single may go out to the bar scene, and may party lots, chat lots, and carry on. Once they find 'the one',..they stop a lot of those behaviours.
The key is, in talking to your significant other, and asking some deeper questions, on why they feel this way. Someone who views their former experiences as part of 'the path' that led them to find what they really want, sounds quite in tune.
Someone who is offering to settle, just to please you and keep you....Well, that could be a different story all together.
Find out if the experiences were part of what that person believed was representative of them, or behaviours as they were learning about themselves. There is a definite difference. Good Luck.