As posted by Zlatica, "Otec" means "Father" and is on many cemetery stones, just as "Father" is on stones in cemeteries where English is the language. "Matka" is "mother". "Syn" is "son", but "Synek" could be either "little son" or a bona-fide surname. So it's remotely possible that "Otec" is the genuine surname, but would be very unusual.
The grandfather of my good friend from high school (we graduated 50 years ago) refused to tell his family his real name because he also left under some circumstance which he never told.
Ancestry also has Albert Otec, but coming through Canada to South Dakota between 1900-1913. Apparently the original record has a birth date and place, but the image is not on Ancestry. I did a search on all Fran* born between 1872 and 1876 and arriving 1900-1904 and only came up with one that could have been a possibility. (snip attached). I can't read the occupation.
Do you have any other data? Like where did he live for the various censuses, etc.?