Is there some subtle, underlying context to that congratulations that I'm not getting? “Congratulations... for not offing him & allowing him to reach this age!” “Congratulations... for putting up with him for another year & not running back, screaming, to the UK!”
If I was his mother I could understand the random congratulations “Congratulations... for birthing him & for him reaching a ripe old age”. But as a girlfriend, well it just seems a little weird.
Mind you, there's a lot about the Dutch I find weird.