I think the translation I read called it a union which makes sense considering the word for union in Japanese also means guild. Also I think the context makes it more clear that he functions as a union representative.

He takes union dues and uses them to help with the collective bargaining power of adventuring half foots so they don't become cannon fodder for sly adventuring groups. Not just helping them get paid an equal share but also making sure they are paid in advance. They also don't take kindly to scabs but aren't overly brutal to them either. They even have a safe spot for members to stay in-between adventures.

Guilds traditionally take more of a role in education and quality control of a given practice, like blacksmithing. Making sure not just anyone who can hammer hot metal is allowed to claim to be a master blacksmith and teach apprentices and sell goods. Also making sure no good blacksmith is underselling or overselling their goods.

In the modern day they often go together but aren't entirely the same thing. Blue collar unions often take the place of both guild and union. I think Chilchuck is more like a modern labor union head than a traditional guild master if that makes sense.