How can we know? Because if they were pro small business they would be pro universal healthcare, so that it would be easy to start your own business.
I suspect the "right" is actually sincere. But it so happens that ideas giving more power to private businesses tend to disproportionally benefit larger businesses over the smaller ones (this is a natural advantage of having scale and capital). The ideas surgically targeted to benefit smaller businesses? The "targeted" aspect tends to pattern-match to the "left", so they get rejected. The end result looks like the "right" was dishonest, but IMO it's just the ass-backwards stupid fixation on ideology over problem solving that causes this. And the same thing applies to the "left".
It should be like the green new deal - the economics of eg Medicare4All is similar in that it’d greatly improve life for small business as well as families.
None of which means it isn't true (it is), or that it isn't important (it is), but that's why it doesn't get used as an argument very much.