That’s 20 hexadecimal, which is 32 decimal, which is the ASCII code for a space.
Most operating systems, ones whose designers realize that pointing and clicking isn’t the only way to do things, don’t allow spaces in file names, because on a command line ‘words’ with spaces look like multiple words.
The HTML standard uses plain ASCII, but allows special characters to be written as a percent sign followed by the hex value of the character. Your browser (or operating system) seems to be displaying the underscore for the percent sign, instead of interpreting the sequence as a single character. If it doesn’t cause any problem, don’t worry about it. Maybe try renaming the file with spaces or underscores.
Bob the Random Expert
“If we don’t have the answer, we’ll make one up.”