I disagree, as both an engineer and a manager.

CSS grid is only recently becoming a reasonable tool to use in practice. I don't think any of the top 1% of front end engineers I know would be able to use CSS grid without looking at the documentation.

Based on experience, the kind of person who would be able to use it from memory either 1) is very skilled AND had a reason to use it recently, or 2) someone of medium skill who just recently read the spec but in almost all other ways is less skilled than the people I mentioned in the first paragraph.