The results page layout, and how the name is displayed does not affect the sorting, it does no effect.
If the primary sorting is set by '_sku', it means that for example if you type in '101-0100', then no matter where the match was, it will be ordered by '_sku': https://i.imgur.com/ussuvon.png
(this is same on the results page, it's just an example)
The ordering is correct as configured (_sku ascending):
The ordering is applied after the search, and because '101-0100' matches other products in the product content, it displays those as well, ordered by their SKU.Best,
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