Nonsense. The optimization they are referring to is not premature in any sense of the word. If anything, it's belated and overdue.

In any case, the originator of the phrase, Knuth, specifically said that it related to "small efficiencies".

Nobody would call Electron's efficiencies that need to be addressed, "small".

There's a good discussion here: http://wiki.c2.com/?PrematureOptimization