Why was my radiator cap loose?

So recently I was driving home from work and my heck engine light came on. Fifteen minutes later I am home and I take a look under the hood to see coolant splattered all over the engine and my coolant reservoir is empty…! After it cools down I go to take the radiator cap off and it is already loose. I do not drive much, and luckily it’s been very cool here recently, so I’m hoping there wasn’t much damage. I’ve driven only back and forth to work 15 min each and it’s been between 35-55 degrees here. Now my question is why the cap was loose. Can this happen on its own? Is it bad? Or is it more likely that the cap was left loose during a service at my shop 3 weeks ago? The cap is on firmly now and obviously I added coolant, and I haven’t had issues since. Thank you in advance for any insights ya’ll may have!

When was the last time it was in an auto shop? This is for anything, including an oil change.

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No, highly unlikely the cap could loosen by itself. It is quite possible the shop may have, for some unknown reason, opened the cap and failed to tighten it.
Doubtful you did any damage.

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Many times a mechanic will check all fluids as a courtesy. It’s just part of looking after the vehicle. It could have been an honest mistake.

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Service was done 3ish weeks ago

Probably the tech forgot to tighten it during your last service.Engine vibration probably unscrewed it even more until coolant poored out.

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