If a) you actually got it to a rolling boil for a sufficient time (some teas recommend heating to less than boiling temperature), b) the water boiled in the cup (as in, microwave rather than tea kettle you may have let cool a while before actually pouring it in the cup), and c) you took surgeon-like steps to avoid contamination during and after the steeping process, I’d imagine it’d be just as sterile as any thing properly sterilized by boiling would be.
If a) you actually got it to a rolling boil for a sufficient time (some teas recommend heating to less than boiling temperature), b) the water boiled in the cup (as in, microwave rather than tea kettle you may have let cool a while before actually pouring it in the cup), and c) you took surgeon-like steps to avoid contamination during and after the steeping process, I’d imagine it’d be just as sterile as any thing properly sterilized by boiling would be.