it looks like a mold (botulism is invisble and odorless, + they don't form colonies like this, but as a precursor of spoilage that could lead to it, yes)
something was contaminated somewhere in the process (maybe not a fully sealed/sanitized lid if none of the others are like this)
it probably will not result in your demise, but it may induce vomiting and seizures
depending on your ingredients in the jar the smell may not be noticeable, but will become apparent the more it is exposed
like when they open you up and suddenly you have cancers growing