Well like you said, you were farming XP ... it's not really "helpful".
Is it reasonable grounds for a ban ? I can't really tell since I wasn't there. If he warned you many times and you didn't comply then that might explain the ban. I always ask people to get a stick or a practice dagger so at least they spawn with a weapon. Afterwards they do as they like (exchange it for something better or keep it and "try" to hurt anything). Farming gold my doing suicidal runs is considered leeching as you're not helping your team. At lvl 17 you should be able to have a good weapon and help your team, if you were lower I'd understand you "farm" but it's not really helpful for your team to farm if you could actually participate with better gears.
And this is the 100 Battle server section, you'll have more chance for a reply to post in NA (ATS) section in Ban/Unba Requests