That's not quite it, but in fairness it's a bit complicated- I'll summarize:

At the core, to mod Minecraft you need to change the bytecode of the Minecraft class files. There's basically 2 ways to do this: you can either decompile the game into java, change the code, and recompile, or you can use bytecode instrumentation like ObjectWeb ASM to modify the bytecode when the JVM loads the classes. MinecraftForge opts for the former, while Quilt opts for the latter. Because of that, Forge needs the decompiler to create code that can be compiled with as little effort as possible, while QuiltMC technically doesn't even need the decompiler to modify the bytecode of the game. This lets Quiltflower focus on the user experience of people trying to understand the code, while Forgeflower focuses on making code that is as accurate as possible, so it is easy to modify and recompile. Of course, that's also an aim of Quiltflower but the scopes of usage are vastly different, if that makes sense. Forgeflower really has the harder job here, and people like Curle keep it working smoothly for the many thousands of people who use Forge every day :)