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 just boiled would be.