Supervisor does not ask for opinion of graduate student about an undergraduate thesis that the graduate student assisted with
In general, supervisors should "acknowledge" their students more. We often forget to tell people when they are doing well and only point out mistakes.

Your supervisor should have most definitely acknowledged your help with the student. He should have thanked you for helping out with the student and ideally given you feedback about your supervision.

As for comments on the thesis, depending on your official role and the rules of the university/department, he may not be able to talk to you about the grades of other students. That said, he could acknowledge you to let you know that. If he is allowed to discuss the grades, it can be a learning opportunity to talk about the process. That said, grading is generally not a fun part of the job, and he may simply be "protecting" you from an aspect of work. It is not out of place to talk to him about the thesis (either the final product or grade). He will let you know if the conversation goes someplace it should not.

The one place that he should most definitely try and acknowledge you is to the external referee. Something as little as "a lot of this project was managed by my PhD student Billy Jean" can help your networking.