Can you spot the mistake? It’s funny how the brain works – writing the word “buidling” instead of “building” is just an example. Apparently if you have all the right letters and the correct first and last letter of the word, your brain can unscramble it. For instance if I write :
The qcuik bowrn fox jmpus oevr the lzay dog?
You should still be able to read it.
Spelling only became regularised when the dictionary arrived. Once the spelling of words was written down with a definition the spelling was more fixed. But spelling is still quite phonetic, based on sound sometimes. For, four, fore all sound the same but have different spellings and meanings.
The example above is more likely to have occurred because of a computer mistake when the author or designer did not proof read the art work.
I guess I make a lot of mistakes too. I do rely on spellchecker but even that gets it wrong sometimes.