What would cause an octopus to come to shallow waters?

I was at the beach the other day swimming and I stayed in the shallow part because I saw a big fish and got scared, so I was just looking underwater when I saw an octopus!? it was at the bottom of the water on the ground rocks just going about. it was so shallow it almost was out of the water. it was morning/daytime btw.. and it was a small octopus too. super cool but very confusing