"we are total different " seems to be rather a question of different history and feelings rather than actual massive differences regarding to their origin.
You are right. Besides, there are many dialects in Silesia rather than a standarized version of the so-called Silesian language.
No wonder they feel different as they had lived outside Poland's borders for about 700 years. There was a remarkable number of Polsh economic migrants to Upper Silesia in the 19th century which strenghtened the Polish-speaking population there. These people adopted Silesian dialect later on rather than vice versa.
For a Pole like myself it is quite easy to understand Silesian dialect since I know a bit of German. But quite often, they use old Polish/Slavic words that no longer exist in Polish and would be strange to a Pole.
On TV there is a show on Silesian cuisine in which the cook speaks a softened version of Silesian. The way he speaks sounds really funny. For example he says: A teraz przirichtuja ten dressing
, which is in fact a mixture of Polish and German and English (teraz - now; przirichtuja - ich mache richtig / I will make ready; ten - this; dressing - dressing)