One of the jobs I have applied the hiring manager (tech lead) wrote me an email to discuss the position more. So after a week I had a 40 minutes good Skype talk (he didn't turn on the video) with him. He didn't force me much he was friendly and didn't examine me with hard technical questions. And at the end he said he will invite me to the company show around and talk to other colleagues.

My problem is from the beginning he never use the term interview at all. So should I consider my self as I passed the first interview or it was just a talk? Are such Skype or phone dialogues under the category of "first interview"? Or there is no consensus about it?

The reason I'm asking because I try to figure out whether I should prepare as I am going to the first or to a second interview, if he really invites me.