If you're going to have an interview with a CEO that had international experience with important companies (ie: Google, Skype) would be appropriate to ask him about differences with his current position in a smaller european company? Or it seems like I stalked his cv?
If you are interviewing for a job, it is perfectly acceptable to ask questions. However, only ask the question if the answer will help you make your decision.
Why do you want to know about the differences between BigCorp and his current company, SmallFirm? Is there something specific you like or don't like about BigCorp? Then be specific about it! Say, "I saw that you used to work at BigCorp, and I know they like to use Widget X. Is that something you use here at SmallFirm as well?"
If you are curious why the CEO left BigCorp to begin with, because you have always heard it's a great company, then don't ask the question. The answer could be very personal to the CEO, and will really tell you more about BigCorp than SmallFirm.
Unless you have previous experience or knowledge of BigCorp, then don't ask the CEO to compare the two companies. Ask questions that will help you learn about SmallFirm independently without having to compare to something you know nothing about.
You didn't "stalk his CV" - you performed due diligence on the company you might be going to work for.
That being said, you should ask questions that pertain to the current company during the interview, not his previous positions.
- I read about the XYZ management process that was developed at Google while you were there; are you implementing that at Current Company?
Seems like a decent question but you could frame it better.
What did you learn from working with/at Google?
Is there anything you will/will not apply here?
Any big lessons?
That's assuming you do actually want to know and have will make use of the answers you get. Otherwise it just comes off as fluff/stalking/hero worship
Normally when you're going to see a CEO, he/she is the one asking the questions, and the dialogue is work related. Only if the conversation is very casual and friendly and there is no time pressure would I ask such questions during an interview or meeting and even then I probably wouldn't unless we had nothing to talk about. It's best to focus on the subject in hand, rather than go off on a tangent. This gives the wrong impression.
Typically I would only ask in a non professional setting (we're both outside having a cigarette for 10 minutes or something similar).