Jhill

Yes you are absolutely being paranoid. Oem spring clamps are usually much better grade than after market screw type. Also all the other bigger hoses will be using a much more robust spring clamp, the one on the little hose is just the wimpy flat spring steal not like the bigger thicker clamps.

As for your professional tech I can tell you what probably happened being I came from the industry. They usually get paid on a system called flat rate so paid per job. Probably got paid for the inspection saw the coolant and then given no time to diag so just threw a cap at it. Not saying it is right but it is what happens which is why I am a huge opponent of flat rate shops. If tech follows the proper steps then they make no money if they cheat they make more.