Is that true? That's not how I understood it, and sources I'm finding online seem to agree e.g. https://aas.org/posts/news/2017/08/month-astronomical-histor... and https://research-repository.st-andrews.ac.uk/bitstream/handl....
At this late date I would expect most accounts to be written as if it was obvious all along that "Vulcan" wasn't real. It was announced as discovered at one point, so it was not at all obvious at the time.