Well, for starters, this is (supposedly) a "gift" to a TSO and not the entire TSA. The TSA, as an entire organization, could "substantially affect" the City of Atlanta, but the TSA can also deem this gift to be ethical per the same law you just selectively quoted.

You're setting the bar pretty low if you think that the City of Atlanta is "substantially impacted" (or would even notice in the first place) that a single TSO comes in (or not) to work.

(Never mind that the whole point of this law is for the appearance of objectivity in business matters with the government, which again doesn't apply here since a TSO work attendance is unlikely to impact the City's ledger).