Low-tier adware families often create folders with alphabet-soup names in %AppData% or %Temp%. The string xfadsk2018x64 has no linguistic pattern, making it suitable for such use.
System administrators sometimes use placeholder names like testfile2018x64 when writing batch scripts. If a junior admin typed xfadsk2018x64 by accident (e.g., mashing keys to avoid naming conflicts), that name could propagate into log files or temp directories. xfadsk2018x64
If you encountered this string, it was likely part of: mashing keys to avoid naming conflicts)