Definitely not metalcore. I can see how it might come off as metalcore because of the vocals. Here and there it shows when he pronounces Y's and Ow's in somewhat of a chaotic way, but his vocals have that bareknuckle snarl whereas metalcore lacks that ballsy presence. Sil Veth's music is too progressive to be metalcore also. Here are some metalcore bands:
Shadows Fall
Killswitch Engage
Hatebreed
As I Lay Dying
There is a huge difference seen in metalcore when it comes to the other genres. Metalcore does have emo and obviously "hardcore" within it's inspiration and that shines through a lot within the music writing process as well as the vocals. The metal part within metalcore are the simple guitar harmonies and the short bursts of blast beats usually falling into some sort of breakdown slam beat. A little above elementary when it comes to skill, but talent is where they lack IMO. It is full of melody but nothing worth appreciating musically. The vocals can be spastic with no direction or control. However, clean vocals appear often, but come across as whiney and appear to be pussyfooting around the music. Metalcore is metal for the masses. People who cannot comprehend talented, well-thought out music result in listening to metalcore.
Someone uneducated (or stuck in the unfortunate nonbelief) in the study of metal genres can get these things mixed up. However, there's no way I can see how anyone can get bands like Shadows Fall mixed up with Sil Veth. Keep kicking ass.