This generator shifts every printable ASCII character into Unicode's Fullwidth Forms block, a set of characters originally created so Latin letters and punctuation could line up neatly in a fixed-width grid alongside CJK text, and swaps regular spaces for the ideographic space character to keep the wide, evenly spaced look consistent. That's the same trick behind the "vaporwave" text aesthetic popular in bios and captions. Because it repurposes a block meant for a different script, actual letter spacing and the width of the ideographic space can render a little differently between apps and fonts.
The wide, evenly spaced look produced by Unicode's fullwidth characters became closely associated with vaporwave-style aesthetics online, even though the character block itself was originally designed for lining up Latin text with East Asian typography.
Regular spaces are swapped for the ideographic space character (U+3000), which is designed to match the width of a fullwidth letter, so it looks noticeably wider than a normal space.
Yes, the whole printable ASCII range, from "!" through "~", including digits and common punctuation, has a fullwidth counterpart, so it all converts along with the letters.