Yes, well, seniority tends to be defined quite differently by management – compared to how other devs would define it. A senior to them is a person with a certain experience (at least 3-5 years), who has worked on at least a couple of complex projects (no telling exactly what they did there), shows a "can do" attitude, has good feedback from teammates, and last but not least delivers stuff on time.

Notice how quality of code doesn't come into it at any point.

Management doesn't know which code is "quality", it's all voodoo to them anyway. A pleasant team member who sounds like they know what they're doing and delivers working stuff is all they need to see.

Quality of code needs to be defined and enforced on a project-by-project basis (definition of ready, definition of done). If they aren't defined and/or enforced, but delivery still happens on time, it will be hard for a junior to demonstrate a problem. Some experienced managers will recognize it as a problem in the making by accumulating technical debt, some won't (or don't care).

I would suggest that OP explains the technical debt in impartial terms during sprint review and wash their hands of it. Confronting the other dev directly usually doesn't work well, especially if it's done remotely.