Yes, any laptop without an encrypted storage drive will have its data accessible by someone booting from a live USB.
It really is a massive vulnerability, but it's not well known because so few people even understand the concept of a 'live USB' to make it a widespread threat or concern.
So yeah, if you're ever in possession of a Windows machine that doesn't have an encrypted disk, you can view the users' files without knowing their password via a live USB.
It's also not limited to laptops.