Those are SRG names. Minecraft vanilla is obfuscated (a.a, b.cf, ee.q) and so the deobfuscation process translates those names (which change every version) into a consistent pattern of SRG names (that don't change often, if at all) before being made human readable by replacement with MCP names.
MCP names are entirely human generated as a community effort. If an MCP name does not exist, then the SRG name is used.