By the power of truth, I, while living, have conquered the universe.
We've seen this exact same ability in Halo 2 with the Fist of Rukt, as Tartarus had it augmented with Forerunner technolgy which allowed him to do things like grab and suspend things in the air - at the end of The Oracle, for instance, where he uses it on 343 Guilty Spark.
It's not telekinesis, it's technology and we've seen plenty of examples of how the Forerunners, as a Tier 1 race, are masters of gravitational forces both natural and artificial. What exactly is so alarming about the Didact having the ability to use it on John when we've seen this kind of containment feature for years?