Should I tell his estranged parents that he is in hospital behavioral?

Should I tell his estranged parents that he is in the hospital for mental health problems?

My 35 year old son is high school pals with P. I know P and his parents. P got angry with his parents and stopped talking with them about a year ago.

Yesterday, a local hospital left a vague message on my son's phone. He thought it was about me (his mom) or my husband (his dad), so he called us to check that we were OK. We were OK but the phone message got all of us worried.

It turns out that his friend P uses our son as his emergency contact person. And P was in the behavioral health unit of the hospital. Our son told us that the message was about P.

Our son is really stressed about being the contact person. He wants to do the right thing but doesn't know what to do. The hospital hasn't even called back to explain what is going on with P, what will happen, what P needs now and when he gets out, etc. Nothing. Frankly, I have no experience in this area and my husband and I have no ideas.
Except one.

We think that maybe we should let P's parents know that P is in the hospital. Our son thinks that we should not tell them because P has been angry with them.

I think that maybe P's anger with his parents is part of his mental health illness, like a symptom. P has ended a lot of relationships with friends, other relatives (sibling and aunt) and co-workers in the last few years. Our son is one of the last people in his life.

My husband and I only know P's parents socially and from the time our children hung out together all the time-- like all the time, so we heard a lot about P and his family. They seem like really nice normal folk. They were really supportive of P all through high school, college, and his brief marriage and divorce. We don't think that they caused the problem. P is adopted and so is his sibling. Their estrangement seemed to be caused by sibling rivalry, at least in part, from what P told our son. Since I have known P since he was a kid, I did try once to suggest gently that he try again with his parents, but P was not interested. I realize that no one really knows what goes on in a family...But I saw his parents go toe to toe with HS administrators in defense of P when he had an issue in HS one time.

We don't know anything about the hospital except that P is there in the behavioral health unit. We don't know how he got there, when, diagnosis, nothing.

Please, everyone, if you can, take a minute to weigh in here. We want to do the best for P, but we don't know what "the best thing" is.

Should we tell his parents that he is in the hospital or not?

Thank you so much for sharing from your hard-earned experience.