I Have A 6 Week Old Baby. Approximately A Week

I have a 6 week old baby. Approximately a week ago, when changing his diapers, I noticed that his feet twitched for a couple seconds. I later discovered that I can induce the twitch when I press the sole of his foot. I googled this and it is supposedly called ankle clonus and if happens for more than 10 beats (and it often does when I press my son's foot) it indicates cerebral palsy. I immediately took the baby to his pediatrician, she examined him and dismissed my concerns. I was not able to reproduce the twitch , it happens more often when the baby is relaxed but she said that it was normal,she saw it "all the time" and that it would go away by 3-4 months of age. She would not refer me to the neurologist. I do trust her but I read so much horrible stuff about ankle clonus in infants, including one scientific study, that I cannot dismiss it and need a second opinion.
The baby is active and alert, raises head when on tummy, follows me with his eyes, smiles socially and just started to make first sounds. I did notice however that when he makes fists he sometimes puts his thumb between middle and index fingers (abnormal??). Other times the thumb is out. He does open his hands all the time and even grasps at the bottle with open hands when I feed him.
Should I push for a referal to a neurologist? Does it happen in normal young babies?