Was it a big mistake to dispose of mold down my kitchen sink drain?

Burn the house down and start over. It’s contaminated and will never be safe ever again! Just kidding. No, it won’t hurt anything. Mold is ubiquitous. It’s everywhere, it’s already in your house if it’s in the pitcher. It won’t hurt you unless you ingest several hundred pounds of it within an hour or two. (the mold won’t hurt as much as the ingestion) You’re fine, the house is fine, it won’t remain in your plumbing longer than a few toilet flushes. But remember mold is everywhere, and you can’t escape it. It coexists with you all day everyday.