Is it normal for my dad to think my 16 year old sister is "hot"?

My dad and I were looking at pictures of me and my sister from our vacation. We both agreed that I look like a boy and my sister looks like a girl. I'm just an ugly tomboy, I don't mind this. Then my dad said that my sister has become "hot" in the past year. Do dads think like this about their teenage daughters or is this something to be worried about?