Yep - this is like field sobriety testing, in my mind. Everyone will display some level of nervousness and inability to perform all the tests, and the officer thus has a baseline level of "cause". They can therefore do all kinds of tests or hold you until you do those tests. B/c "He failed his FST"
Same with poly. If they don't like something, they can just say "He failed his poly"
I don’t get how “field sobriety testing” in the sense of observing someone perform some coordinated actions is still a thing. In Ireland if stopped by a member of the police (Gardai) and they have suspicion they can require you to provide a breath or saliva sample. If you pass you are free to go, if you fail or refuse you are escorted to a police station and provide a blood sample or urine sample (I think this depends on if suspected of alcohol or drug offences) refusal to provide the sample is an offence
Same with poly. If they don't like something, they can just say "He failed his poly"