Arrested for stalking but don't know what exactly I'm accused of doing

I messaged somebody who I knew who was a friend of my circle of friends.

I did not believe I was committing a crime and I wasn't stalking them. However they went to the police which I think was done maliciously because I don't think there was anything wrong with what I said.

The police arrested me for stalking but I haven't really been told in a meaningful way, how what I did was stalking.

As I was being booked in at the station, they briefly mentioned what I had allegedly done but I can't remember any of this because I was in shock, the same with the interview.

I was hoping i would get something in writing formally that said what the police believed I did that was stalking.

As of now, all I know is they arrested me for sending some messages and that they had it down as stalking. But no explanation of how it was stalking.

I don't know what even counts as stalking in the eyes of the law. To me, stalking is like spying on somebody or following someone around/constantly going near them without consent.

So you might be able to imagine that I am pretty confused as to why I was arrested, held in a cell and had my phone taken.

Yes I sent some messages, apparently they didn't like them but I don't see how that's a reason to arrest somebody. People say things that other people don't LIKE all the time, and wouldn't that be harassment, if a crime at all?

This person isn't an ex or a partner. I've not followed them or tried to go near them. I just sent some non offensive/threatening messages to them (which I don't disclose for anonymity reasons)

So my question is, is there any way I can get a explanation from the police about why they believed I stalked them for them to justify arresting me and taking my phone?