Nope, that's what wood (especially pressure treated wood) will do. It will get worse too.

Yes you should be concerned. Splitting is normal, but that post wasn't well cured. A lot will depend on what kind of climate you have and what kind of wood this is. If this is pine in a warm and wet climate, being pressure treated will not prevent it from rotting for any length of time. If the splits go below the decking and into the ground that is even worse.

I'm also wondering what's going to happen when high winds hit that big top - it doesn't look like something that you would be taking down and putting away during bad weather. Also the covering - reeds? bamboo? - doesn't look like something that would last through an extended period of year round outdoor exposure. Except maybe in a desert climate.