Think it's because the comination of a number and your annalyzer type:
Simple – divides text at non-letter characters, including numbers. The dividing characters and any words that consist of them (for example multi-digit numbers) are not included among the searchable tokens.
Try playing around with the Analyzer type: https://docs.kentico.com/k12sp/configuring-kentico/setting-up-search-on-your-website/using-locally-stored-search-indexes/creating-local-search-indexes#Creatinglocalsearchindexes-Reference-Searchindexproperties