The Montana Death Index includes a Matthew Sanders who was born ca 1858 and died May 20, 1931.
As you probably already know the family was in Belt in the 1900 census. It shows he immigrated in 1884 and she in 1886. They were married 16 years. He was born in Austria.
The 1910 census shows a Mathew Sandor 48 married to Jane 41 living in Roosevelt, MT. They were married 25 years and the children's names match the ones from the 1900 census.
The 1920 census shows them back in Belt. This time he is a widower 60. It shows he was born in Hungary but spoke Slovak. It also indicates he immigrated in 1888 and became a naturalized citizen in 1910 probably there in Montana.
The 1930 census shows Matt Sandor 72 widower, immigrated in 1880 and born in Czechoslovakia and his nationality was Slovak.
I'm don't know how interested you are in finding more, but his death certificate would probably tell you his parents and possibly where exactly he was born. His obituary would probably help too. His naturalization papers probably have the exact date and place he was born, when and where he arrived and the name he originally had. Sanders is as far as I know anything but a Slovakian surname.
Just in case you aren't aware of it Slovakia was of course part of Czechoslovakia from 1918 to 1993. Before that it was part of the Austro-Hungarian Empire. This would explain why he was shown as born in Austria, Hungary, and Czechoslovakia. Of course I'm assuimg they are all the same person in each of these records.