>In this particular situation, the discussion never got past the first question. I needed to understand why our checkout had to be improved; I explained that technology choices made no difference to the user. However, the manager interpreted my words as outright rejecting their idea.

Well, it was "outright rejecting their idea".

Whatever the phrasing used, the actual question wasn't "Would it be technological better and improve the user experience if we use React for our checkout UI?".

It was rather "I read about this React thing. Sounds cool. Cool companies use it. Should we use it ourselves too and be cool like them?"