To help users familiar with gdb's existing CLI interface, gdb/mi accepts existing CLI commands. As specified by the syntax, such commands can be directly entered into the gdb/mi interface and gdb will respond.
This mechanism is provided as an aid to developers of gdb/mi clients and not as a reliable interface into the CLI. Since the command is being interpreteted in an environment that assumes gdb/mi behaviour, the exact output of such commands is likely to end up being an un-supported hybrid of gdb/mi and CLI output.