This problem was even worse: it's matched by the formal grammar, but the naïve formalisation has a trivial answer, so it is clearly not what was intended.
That clearly may be doing some heavy lifting. It is assumed that trivial answer wasn’t what was intended for the problem, but unless someone asked Erdos, I don’t think we know.
Considering that he did some work towards the problem, tackling non-trivial cases, I think we do know. There's no way he wouldn't have perceived trivial solutions at some point.