Halving or doubling is entirely feasible, though unless you're experienced go with 1x the first time you make the recipe.
In this case the ambiguity is a factor of 3X, the difference between a teaspoon and a tablespoon. Or possibly more: given the quantities of the recipe he may mean some kind of personal dedicated spice spoon that could be around 1/2 tsp. In which case a tablespoon would be a factor of 6x, which is sufficient to make a recipe inedible.
If that recipe appealed, I would say that if you use a teaspoon the recipe would work (assuming he hasn't made other errors in the recipe; I didn't look that closely). But he's not following the conventions and I'd probably go looking for a difference recipe.
Once you've made a few recipes successfully you can, as you point out, easily halve or double spices. But I'd start with recipes that were better tested than this one.