So, from the summary:
Tekoh was accused by a patient for inappropriately touching her, was questioned without being placed in custody and without being Mirandized (which covers custodial interrogations, not every single discussion police have with people). Tekoh was convinced by a Deputy to write an apology to the patient for touching her inappropriately. This statement was used as evidence against him in his trial. Tekoh's first trial ended in a mistrial and he was acquitted in his second trial. Tekoh's lawsuit was a section 1983 action seeking monetary damages because he believed his civil rights were violated.
If Tekoh was not in custody (which, I don't believe he was) and was not being coerced, compelled, or abused to extract a confession, then I guess I don't see the fifth amendment issue. If I had to imagine details not presented in the summary, I'm guessing the Deputy told Tekoh that a decent person would at least apologize for doing something that offended someone, and it is likely that Tekoh believed he was simply disarming the situation as opposed to providing evidence to be used against him. If the argument was that the evidence shouldn't have been admitted or something then I could probably be swayed, but the idea that Tekoh should get a payday by labeling this a civil rights violation given the circumstances I don't think I agree.
This decision does not seem to be saying that cops should be able to beat you to get a confession, or even commenting on whether a confession made outside a Miranda warning should be admissible, but rather seems to be simply saying that failing to read someone their Miranda rights before conducting a non-custodial interrogation should not be sufficient to allow Tekoh to sue the Deputy and department for violation of civil rights.
Am I missing something?