I don't believe he has just 5 losses,he is no Lomachenko.You can look in boxrec and compare partial record and see there are similarities.
The partial record on Strefa is correct but incomplete. 345-5 is something someone pulled out of his ass and somehow it became the truth.
The Strefa site is AS GOOD a source as you will get for amateur records. They often have the competitions where the bouts took place for cross reference. Easily more reliable than the people who scream 345-5