I found this article that explains that the arrest warrant was only to be activated if Pavel was on the French territory.

(French) https://www.sudouest.fr/economie/reseaux-sociaux/le-patron-d...

It could have been a warrant that was not communicated to Durov himself. This would have helped to catch him by surprise.

The Sud-Ouest article must have been updated because the version currently online does not mention that at all. Quite the opposite, the article quotes an official that was surprised that Durov would come to Paris anyway even though he knew he was under an arrest warrant in France, and another source says that he might have decided to come in France anyway because he believed he'll never be held accountable.

yeah so sounds like (what in the US we call) a sealed warrant, not that it was literally issued while he was in the air