This is a good question---from the logical point of view, a scalar is not an object of the same "type" as the one by one matrix you can make from it. (I have just spent hours trying to compile someone else's code which won't compile because of similar type errors.)
From the physical point of view, there is no difference if they both can be used for the same purposes. Which they can, in this context.
As far as I know, they can always be replaced by each other in every context I can think of in physics.
The "purpose" of a matrix is to describe a linear transformation on a space. A scalar always does act on a space, or it wouldn't be called a "scalar", it would just be called a "number". Usually, the matrix coefficients change if you change the coordinate basis on the space. But the matrix coefficient of a scalar never changes no matter how much you change the coordinates. So they are coordinate-independent, just like numbers are.
To enlarge on this pedantic point a little, a scalar is not quite the same as a number. We only call a number a "scalar" if we are thinking of it in connection with a vector space it acts on,, as a linear transformation. So, if you accept this common usage distinction between "scalar" and "number", the one-by-one matrix IS exactly the same type of thing as a scalar, but is not the same type of thing as a number. The real sloppiness, which is harmless, is to think scalar=number. If you accept this distinction, then there is no sloppiness, even logically, in saying the product of those two vectors is a "scalar". And that is why it is called the "scalar product". But it is not exactly a number (if you accept this distinction).