[30M] and [30F] in a relationship for almost 2 years random girls at birthday

So my boyfriend just had his 30th birthday party, it was super intimate. Family (cousins + close aunts/uncles) and a few friends (6-7), my parents were also there. One of his best friends brought the girl he’s seeing, this was the first time the rest of us, including my boyfriend met her. She was very sweet and I welcomed her kindly. Later on I overheard her saying to the rest of the people that she had a few of her girls coming over to the party, I asked my boyfriend privately if he had approved of this. When I asked him, his response was yeah my boy asked me if it was okay for her to invite some of her girls over, and my boyfriend said yeah it’s fine.

His reaction was that I was overthinking it, he got a bit annoyed with me for being upset and he said his reasoning was that the party was so dead since there was hardly anyone there he said fine to her bringing her girls. He said that’s how parties usually work and it’s not a big deal. My reaction was quite different. If it was a big party at a club or something I wouldn’t question it, but these random girls were going to show up to his house (to his very intimate birthday party). I felt uncomfortable that he said okay to this without even asking me or telling me first - I found out by overhearing the others talking about it. I don’t even know the girl his friend is dating, so why would I feel comfortable with a bunch of her girls showing up to his house for my boyfriend’s birthday.

Am I overreacting or am I valid?