Steve Wright is right on the money.
The courts assume you are legally innocent until proven guilty beyond a reasonable doubt.
The police can approach you and start a conversation, in an effort to investigate you, without so much as a scintilla of evidence against you.
If they have a reasonable, articulable suspicion that you are connected to a crime, they may briefly detain you; if concerned for their safety at that time, they may briefly pat you down. This isn’t even “probable cause” - it’s just something more than a hunch. It’s a common-sense concept where the officer can point to specific facts which, taken together, reasonably indicate suspicion.
If the police have probable cause to believe you have committed a crime, you may be arrested. Probable cause is not anywhere near “beyond a reasonable doubt” – it is merely evidence to indicate that a crime was probably committed, and the accused probably a guilty party.
In short, the police have no obligation whatsoever to “assume you’re innocent until proven guilty.” That obligation rests upon the finder of fact at a criminal trial.