Is the cap on the coolant overflow tank faulty?

Hello,

I opened the coolant reservoir on my Golf yesterday after it had been standing for two days. The system was under pressure, and some milliliters of coolant sprayed out. Could it be that the valve in the lid is faulty?
Water level and visibility were okay; the vehicle was moved within two days approximately 1200 km from the 'container opening'.

Greetings

Tobias

PS: I didn't specifically pay attention to the bundled hoses, meaning they didn't immediately catch my eye.