As your math. suggests it comes down to mere semantics.
Do you call a bet with a roving banker and three others a single bet or a multiple bet? The end result is the same so I would call it a single bet.

However!!!

If you want to have correct statistics AND want to know which of your selections perform badly, or well as it may be, I would record them separately like: first/sec. first/third, first/fourth etc.

You may find that some of them (in your horse selection) are not worth considering either as a rover or as second etc.

Good luck