Main thing is, the IRS rules I see pertain to employer handouts or offerings. They can be qualified as fringe benefits (with a lot of lingo.) From the IRS pub, my italics: “However, if your employer gives you cash, a gift certificate, or a similar item that you can easily exchange for cash, you include the value of that gift as extra salary or wages regardless of the amount involved.”
A gift card from someone who works in the building, not the employer, is not earnings, in any way I see.
OP is not the employer.
Nothing is on record. It’s not an employer expense. Not income.
And not traceable. How would the IRS know to pursue this?
The restaurant situation is different because minimum wage laws apply differently to jobs where tips are expected/customary, as part of earnings. (Hourly wage is a “sub-minimum wage.”)