If they call you it means they are checking city or county records for approved building projects and are fishing to get the job. obviously based on what you said if someone posted building plans for bids they would know why the company was calling and would not be posting here. AVOID companies like this as they are rarely local and will resell your job to another contractor at a profit without lifting a hand, which in the final analysis means you paid too much. AVOID.
They called me too. I know them, it's a Bid Clerk Company. Theit site is www.bidclerk.com
The generate construction projects and post information about them for bidding,though in order to get blue prints or detailed info, you have to subscribe.I used them for my company.There is also a section for homeowners where they can post their home project for contractors' bidding (not sure about the fees for homeowners).
If they call You, that means You posted Your project for bidding on their website or You own a construction company and they want You to subscribe :-)
I also use them for my construction company. They actually have really good customer service, so next time they call just pick up and tell them that someone must have accidently used your number for their account, and they'll take you right off.
This company fishes through building department records looking for recently submitted or approved jobs and contact the owner or developer to bid on the job.