The thing that's either confusing or revealing (depending on which way you look at it) about this announcement is that the name of the carrier will only be announced next week. So bookings can't be made before that date even though the first flight is just over a month from today.
I don't think any of the established carriers (like Flybe or BA) would need a week to add a new destination to their booking engine. Which leads me to believe it's neither of those and we might actually be looking at VLM. Which knows the route well of course but doesn't have anything resembling a decent booking engine right now. Their site is very incomplete and still shows flights from Maribor that aren't bookable anymore. So they might indeed need a week to set something up for the ANR flights.