Altium might do stupid thinks, like trying to integrate the FPGA tools in their PCB software, but I don't think they would do illegal things like selling your designs to competitors. I know FAEs of other vendors are contacting companies regularly, e.g. Altera. They know their customers and applications, they know what their new chips and software can do and even if they want to sell their their products, it can be useful for both sides. But if you don't like this, you can just say "no thanks", unless the PCBWorks license agreement has some creepy clauses.