The topic you linked doesn’t contain any code snippet, but an embedded (“one-boxed”) link. The content of the post only has this link:
… and I guess it’s impossible to extend the forum search to also crawl all embedded links in the forum, as this would get complex very quickly.
But you can always ask/suggest on meta.discourse.org about improving the search functionality of the Discourse backend.
When looking for code specifically in any part of the the ImageJ/SciJava/ImgLib2 universe, you can also use the GitHub button on search.imagej.net