They would have very limited visibility even if they went out of their way to configure it; on top of that, I would not expect them to do so.
They could scan your network and identify devices by IP and host name; a good scanner will often identify OS as well. Active measures of this sort are (a) detectable and (b) highly uncommon on user workstations. Restrictive firewall rules may limit detection, but Windows was discoverable on the public profile by default the last time I checked---just the machine itself, though, not details like shares/applications/services.
If they put their NIC into promiscuous mode, they could listen to any broadcast traffic on the network. Windows devices in particular are noisy, and if your router and computers are configured for DHCP then they could find everything eventually.
In a highly unlikely scenario, their system could run a rogue DHCP server that attempts to route all network traffic through their workstation by presenting itself as the network gateway. This is (a) extremely impractical, (b) unreliable, and (c) detectable. With browser-level VPN, they would be unable to see what you are browsing or downloading even in this extreme scenario. Depending on how your VPN handles DNS queries, they might be able to identify the domain. I.e., your browser must resolve security.stackexchange.com in order to load this page, and DNS resolution is typically handled by the OS. If your VPN traps that DNS query and resolves it over the VPN, then the security.stackexchange.com name would not even be visible.
In the end, it is extremely unlikely that they would see anything significant on your network. If your Windows machines are running default settings, there are some neighborhood discovery protocols that will touch the work machine, and incoming communications are often logged. However, these limited probes reveal very little (typically IP, OS, host name, and workgroup name). Unless you have a specific reason to be suspicious of their intentions, you probably don't need to worry. The level of effort required to snoop effectively is generally a deterrent, and that doesn't even consider the possible legal and PR issues.