The case was dismissed with a summary judgement, which is one of the earliest points a case can be dismissed. Arguing that the action was unreasonable is highly fact specific, and so cannot be done in summary judgement. In contrast, arguing that no seizure occured requires to finding of fact, because there was no dispute of any relevent fact, and so is done first.

That's not how this works. The state moved to dismiss on one set of grounds. That dismissal was granted by the lower court. From there, the case can't proceed until those grounds are settled. This type of thing is very common. It's exactly the same as why standing is established before evidence in civil cases.

It's not suspect, I think you just don't understand how things played out.

If the basis of the lawsuit (in this case the 4th amendment) is wrong, then they should throw the case out at that point.

SCOTUS's job is to determine if the basis for the lawsuit is constitutional or not, they don't determine the facts of the case or anything like that, just if they can sue under the 4th amendment or not. They decided that yes they can.

Now the case can proceeded. This isn't unusual in any way.