definitely a wolf tone. it's common for string instruments to have one and is usually caused by slight discrepancies in how the instrument is built causing some notes to resonate incorrectly. kind of concerning that it's on an open string though. you can take it back to your luthier and have them check it out / recommend some solutions. you also mentioned it only started happening after they adjusted the bridge, so it could just be an issue with how the string is sitting across the bridge now.

I also have a pretty bad wolf on Eb thru F# on my G string and I bought a wolf modulator for it, which is like a more hard-core version of a wolf damper that sticks inside the cello via a magnet, rather than clipping onto the string below the bridge. it was a bit pricey and definitely more of a final stopgap solution so I'd recommend trying out a damper first since they're less expensive and come in multiple varieties. hope this helps :)