Weird for fwb

So my fwb still lives at home with his parents and his brother. Recently I went over and he was walking me out and he’s dad was walking past and he introduced himself and asked how I was getting home and to drive home safe (he was real sweet🥺).

Anyway my fwb was telling me his parents are going away for 3 months and that the girl his brother is seeing will probably come around for dinner often and then he goes “you’re welcome to come over to, whenever you want really, always welcome. We can get some food and eat all together and you can stay the night when you like”

I thought it was really nice to invite me but also I’m confused whether the girl his brother is seeing is actually his girlfriend/if they’re dating or whether they’re fwb because if they are dating and she’s going over is it strange he’s invited me but we’re just fwb? Maybe I’m reading too much into it.