What is this site?

Is this a minecraft discussion forum?

No, it's a free forum for students of Peking University.

https://github.com/pkuanvil/nodebb
What is pkuanvil?

PKU Anvil is a liberal, anti-censorship forum based on NodeBB, built for the Peking University students and faculties. It is intentially not officially affiliated to the university to resist censorship from the "Center for Youth Studies" of Peking University. To read the motivation behind PKU Anvil, see (written in Chinese) the statement of establishment and pinned post - new comers please see here.

however the name anvil does originate from anvil in minecraft

Ally

Right. This site's name is from Minecraft.
For more information, please read this with Google Translate.
@admin 在 [公告] 置顶贴 - 新来的用户请看这里中说：

站长认为，p大急需一个不受青研蛮横管制的，自由的讨论社区。站长于2022年12月2日成立了基于 NodeBB 代码的 PKU Anvil 论坛：https://www.pkuanvil.com，并在次日凌晨开始在未名树洞宣传（第一个宣传贴是未名树洞 #98871）。取名 "Anvil" 是指代沙盒游戏 Minecraft 中的铁砧，是一种使用装备或附魔书的昂贵的附魔神器；“Anvil” 的英文原文是指"有平整顶面的巨大铁块“，我们常见到的纪念碑（此处应有图）就是一种 “anvil”。站长不求pkuanvil变得如何伟大，但求pkuanvil立此为据，能给予p大师生共同所有（而非少数言论审查机构所有的），得以发扬自由思想和丰富人格的试炼地；同时就像未名树洞成立时所说的，真挚的感情是人类最宝贵的财富，希望p大anvil亦能作为纪念种种弥足珍贵的细微感情的见证地。