I responded the way I did for various reasons.
Normally, a "random" onlooker is allowed to report an issue - be it main chat or not. Ie: Someone catches an individual exploiting a bug - totally OK to report! Two people having an altercation and you getting involved and reporting either of the individuals, not exactly. Either of the afflicted parties need to report the damage they have suffered themselves in order for it to be valid. This is the way that law prosecution functions in real life and further should logically here because we are enforcing player-relation rules. So if X is fighting with Y in the Mainchat, you can ask them to take it to PMs, or let them finish it out - no need to get yourself involved in their issue since its theirs.
Now, if you didnt agree with what I said above, then lets look at the situation in dispute. The rule specifies the term "harassment". Let us use a widely accepted source of definitions, Dictionary.com. According to Dictionary.com, harassment is defined as: "
1. to disturb persistently; torment, as with troubles or cares; bother continually; pester; persecute.
2. to trouble by repeated attacks, incursions, etc., as in war or hostilities; harry; raid.
In both defenitions of the word, there is a sense of repetitiveness. In the image (screenshot) you presented in the report, you showed us a single instance; thus failing to meet the "repetitive" requirement for it to meet the harassment requirement.
Now, the rule further mentions that "flaming" would be punishable as well. If we would to consider the fact that someone says: "Player X is horrible at the H class" as "flaming", then we would be overwhelmed with reports of "flaming". Now, does that mean that you can go calling it out repeatedly in public chat, or main chat? Not exactly, as doing it multiple times or persistently in different occassions would then fall under the category of disrespect and harassment.
I hope that you understand the rule a little better now in regards to submitting report tickets.