Essential Oil around newborn

First time mom here..my son will be five weeks on Tuesday. We went over to my dads today and were there for about an hour and a half when I looked up and saw that he was diffusing essential oil.  I asked him what oil it was and he said it was lavender, so I started googling and come to find out you’re not supposed to diffuse oils with babies under the age of three months. He did have his windows open and ceiling fan on and we were in an open living room. But has anyone else accidentally done this?? Can someone please talk me off the ledge because now I’m panicking…