Yes, look like it is.

"It’s based on esbuild’s source, but written in Zig. Zig is an LLVM frontend (like Rust) with manual memory management."

From https://twitter.com/jarredsumner/status/1390084461799170050

It’s not built on ESBuild, but the AST implementation was derived from it, and a related library Peechy is forked from ESBuild creator’s Kiwi.

Sounds like it does everything by itself, in a single tool.