Maybe the drone is flying autonomously and J-20 is observing it's flight/integrity, hence the close proximity.
There's literally any number of reasons why J-20 and GJ-11 could be flying in formation with each other.
What I'm saying is that flying in formation with each other is unimportant either way, if one is interested in their degree of assessing their degree of MUMT development because flying in formation is one of the least important elements and most basic parts of MUMT that they should be well ahead of by now.