That's because this isn't something coming from the AI itself. All the people blaming the AI or calling this a "hallucination" are misunderstanding the cause of the glue pizza thing.
The search result included a web page that suggested using glue. The AI was then told "write a summary of this search result", which it then correctly did.
Gemini operating on its own doesn't have that search result to go on, so no mention of glue.