Competition_open_since - Categorical or Continuous

In Lesson 3, at time 2:14:38 both types of variables are shown - Categorical and Continuous.

I generally use a simple technique to decide which category to put the variable into. I double them and see if doubling makes sense with respect to the variable.

For eg.

  1. Days to next holiday. This variable can have value lets say 2. And doubling this also makes sense. It increases the time duration to the next holiday. Continuous
  2. Day of the month. Lets say the value is 7. You can double it, but just from that you cannot create any more insight. Doubling this variable doesn’t create any new type of information. Categorical

But the variable ‘Competition open since’ does have value on doubling. It should affect the customer footfall in a store. So why is it termed as a Categorical variable rather than a Continuous one.