The census data is reported separately - the 1% threshold for singles is $160K, probably skewed lower because they tend to be younger. If the infographic is based off census data, it excludes single-person households.
So if you are a single person making $160K, you are the 1%. If, later, you get married to someone making $30K you become the 99%, even though the paired earnings haven't changed.
I don't think the graph excludes single-person households. It's certainly easier to be in the 1% with two incomes, but it's not a prerequisite.