@john-c
I'm not entirely sure I understand your writing correctly, but be aware that "Automatic (DHCP)" can mean both SLAAC and DHCP. DHCP can't stand alone on the network - SLAAC is also needed for route announcement, so you either get defaultroute/address/DNS from SLAAC only or SLAAC+DHCP. Never DHCP alone.
Although it is by no means a bulletproof "method", the address part of the last bits of your IP seems a bit too "random" compared to a DHCP-based address - at least from my experience. In the networks I've seen it looks more like DHCP tends to give out more sequential addresses like ::1000:1044.
You've posted a screenshot further up which has two IPv6-addresses assigned. Both a ULA and a GUA. They are almost definitely SLAAC-based as they both have the last 64-bits in common and looks like EUI64-based. Do you get addresses from both subnets on your laptop too?
What kind of router do you have on your network? Is it some Busiess-grade Cisco, Juniper etc. or i.e OpenWRT which defaults to announcing a ULA-network (not that others can't, but not that typical AFAIK).
