Dutch people are notorious for having issues with the th sound, which does not occur in the Dutch language and requires practice. They also don't "soften" leadi

Dutch people are notorious for having issues with the th sound, which does not occur in the Dutch language and requires practice. They also don't "soften" leading consonants, they "harden" trailing consonants like zand pronounced zant. Thus I don't see why your explanation would be likely. Source: am Dutch, would never pronounce titter as dither even with a bad accent. More likely the other way around actually.