Yup, that config is just for the search patterns but that string is used within the parsing of the file in the module code, which is different.
You can see in other Picard submodules that sentieon_algo is often defined to be able to recognise these files. I guess no-one has ever requested this / provided an example file for gatk/base_recalibrator before (also the GATK MultiQC module is a pain to maintain).
Please make a GitHub issue for this and attach an example file