By your logic, the matrix $[1]$ is not invertible, since $[1]$ is the product of the matrix $[1, 0]$ with the matrix $\begin{bmatrix}1\\0\end{bmatrix}$.
The statement you are trying to use is:
If $A$ and $B$ are inverible square matrices, then $C=A\cdot B$ is
invertible, and $C^{-1} = B^{-1}\cdot A^{-1}$.
However, from the fact above, it does not follow that if $A$ and $B$ are nonsquare, then their product is not invertible. If $A$ and $B$ are non-square, then the above fact says absolutely nothing about their product. In fact, as my example shows, a product of two non-square matrices absolutely can be invertible.
However, in your case, the simplest way to think about your problem is using the rank of matrices. In particular, the rank of a product of matrices is at most the rank of either matrix (see this question for details).
Given that, you can answer the following questions:
- What is the largest possible rank of $X$?
- What is the largest possible rank of $Y$?
- Therefore, what is the largest possible rank for $XY$?
- What is the size of the matrix $XY$?