They're putting a chip into someone so they can operate a prosthetic limb. That person can't use the chip to access the net and the net can't be used to access the chip. The people who actually think robots will take over or people will be able to hack someone's brain are just crazy. Neither of those things will ever happen. Mankind has a better chance of building a new Earth out of astroids then robots taking over.
While it is extremely unlikely it is more possible than you realize. They can already alter thought patterns using just magnetic fields. (Read up on Transcranial Magnetic Stimulation.) They can already start directing
some of the actions of animals with electrodes and chips in their brains.
I think we're a long way from sentient computers and robots if that's even possible at all...but as far as hacking people? That is possible to a degree already and will be more possible if things progress as they are.
As far as something using the net and the net not being able to access the chip? That's a fallacy. Internet usage requires
some level of access. It's built into the structure of the net. Packets of information have to be send and received. We wouldn't have had so many tech ideas (including military) stolen from China if it was possible to be on the net with only one way access. Someone always finds a way. There is no foolproof way to connect to the internet and be 100% safe.
All that being said I find it unlikely that people will be taken over, especially by robots. To discount the
possibility though is sort of silly to anyone who researches what they're already learning to do with technology right now.