the patriots arent going to ever cut a player they still value when they can simply IR them instead. whether tarpinians injury is truly season ending or not is irrelevant, the patriots needed his roster spot, IRing him allows them to keep him around for next year and continue working with the team, outright releasing a guy allows someone else to swoop in and take them away from you.
I hope his injury isnt serious, but it really could be serious or it might just not be a huge deal, the patriots might figure they have seen the peak of his growth at this point and it isnt enough, by IRing him for something silly like a headache, they keep him around and also allows them to add someone else to the 53, Free agent deep prospects like Ventrone, Tarpinian and BJGE (as couple of years ago) hold alot of flexibility because their contract isnt huge money and if you make semi-shady moves like this, you can keep them in your system even though they are not on your 53, the patriots have been masters of this for years, last year they probably had 15+ guys on IR and guys such as josh barrett they picked up off of waivers and immediately IRed him, that is really all you need to know.