1. There is absolutely nothing with a man and his wife having sexual relations.
However:
2. The ability of an alzheimer's patient to consent to sexual intercourse is...probably nil. Depending on how late stage the disease is, the ability of the patient even to express his or her approval or disapproval of such things in words is...probably nil (many of them lose the ability to talk).
3. The fact that he may have done it in a room with another patient present is sketchy at best.
All of that said: Alzheimer's disease is an extremely difficult disease. As difficult as it is for the patient, it takes a massive emotional, physical, etc. toll on the family, and especially on the spouse, and if you haven't lived through it (especially as the spouse of an Alzheimer's patient...I haven't, but my grandmother did), then I don't think that you really know what you're talking about, and you should probably keep your opinions and personal indignation to yourself. You just don't understand.
In my view, the guy in question probably shouldn't be behind bars. Did he make a bad judgment call? Probably. Did he do something which, in his precise circumstances, he should be legally punished for? Probably not.