Venting a little coolant doesn’t necessarily mean there is a problem; with older cars I always used to fill the cooling system and let the excess be ejected.

Same with racing dirt bikes , you just fill the radiator up , and let it blow off the excess ( it will only do it the once , till the level has gone down to a certain level ) . Road bikes ( and newer cars ) use an expansion tank which does ensure the radiator stays full at all times ( with some benifits ) , but mostly is just there to ensure antifreeze isnt dropped onto roads .
If the engine was allowed to get a little hotter than it ever has been since the radiator was last filled , then ejecting some coolant will be normal .