C++ – Is returning a reference to inside a private vector bad practice

I have the following trimmed class:

#include <vector>

#include "Tile.h"

class Board {

    std::vector<Tile> boardArr;

    // VVV Bad Practice? Safe?
    Tile& getTileAt(unsigned int x, unsigned int y);

public:

    Board(int width, int height);

};

Note that the vector remains the same size once the class is initialized; I have no methods to modify it. From what I understand, vectors are guaranteed to not move around, unless it's required to resize, so a reference into it should be safe in this case.

From what I can tell, this should be safe. The method is private, so there shouldn't be any way for references to leak.

The best alternative to the above function is to return a copy of the Tile, modify it, then copy the modified tile back. I found using it directly a lot cleaner, so I'd prefer it if it's safe.

This will be single-threaded, and so far, it's only use is to do simple things to a tile, like toggle an internal flag. An example of how I'm using it:

TurnResult Board::flipTile(unsigned int x, unsigned int y) {
    return getTileAt(x, y).flipTile();
}

void Board::setTileFlag(unsigned int x, unsigned int y, bool flagState) {
    getTileAt(x, y).setFlag(flagState);
}