The council could set up a working group to review its policy on communication with yarn bombers and make recommendations to the forthcoming annual meeting. Alternatively, assuming the communication did not cause irreparable damage to the council, either financially or reputationally, rather than voting to change the minutes, members could have observed that they didn't recall the specific request, whereas the clerk did, so the minutes need not be altered.
The key facts, as I see them, are that the yarn bomber has received a communication that may or may not have been authorised by the council and you now have a disgruntled clerk who may decide to submit a grievance. As the old saying goes, pick battles that are big enough to matter, but small enough to win.