Relax my friend, there is nothing to worry about it’s just a declaration that will not affect your application.
Your previous applications are fine, they do not have such a question regarding detention. So let me explain the difference for you, in those applications, they ask about arrests for criminal offenses only so not every arrest applies in this case. When someone is arrested and taken to a police station (as commonly depicted in people’s mind) is really just a detention from a legal point of view and does not start to become an arrest until you are formally accused or charged with a crime, in which case you’d be booked and be subject to questioning ..etc. When the police accuse you or have reason to believe you committed a crime it is always an arrest and needs to be disclosed, however when it is someone else making the accusation outside of the police it is only a detention and you would only have a police complaint against you, not a criminal arrest or charge. It does not need to be disclosed except in your PR. I have no details about your case so I’ll just assume it is the latter.
One thing to note is, police in European countries are known to have very strict retention requirements regarding police records.. They routinely destroy documents and erase data from computerized records after very short period of times when the record is no longer needed, especially when the subject is not charged or found not guilty. I wouldn’t be surprised if there was no record found for you at that police station or at any official agency. If that was the case then there is no way it can be found out in background check or be held against you unless you admit to it yourself, but you do still have a moral and ethical obligation to disclose.
Finally, your PCC is clear because you do not have any criminal convictions, it will not list arrests or charges as such records have no legal value whatsoever (US Supreme Court words, not my words). You didn’t do anything wrong and therefore shouldn’t have to disclose anything but unfortunately things work differently in US/Canada, we have a different policing culture that like to stigmatize persons even if found not guilty.