If they don't own any trademark, they don't have any intellectual property rights, so this is not really an issue.
The type of domain you have bought is a (very) speculative "brandable" domain. However, the most valuable domains are generic terms related to profitable online products and services. You can get an idea of what domains are valuable by looking at
domainprices.co.uk.
See also:
Domain Name Trading Resources
Rgds