Earlier quoted context omitted.
Well it does not matter if it's alarming or not. They are in violation of their signed NDAs with their previous employer. Also, if they don't work there anymore, they should've deleted all the code (if they had it) and surrendered/cleared up all the laptops. But I like your idea, anyway I give big kudos to candidates with their own pet projects.
Almost every employer will violate their employee's rights without a second thought in ways they consider "unimportant but necessary to the business" ... as long as that continues it should be a 2-way street.
I'm an employer right now in my small company. Don't see any reason to screw up my employees, on the contrary, I see it's much better to work in a friendly environment. There's no such "unimportant but necessary to the business" things.