Some people think when a word is spelled correctly but used incorrectly, that is a spelling mistake. I disagree. If a person intended to use a different word, but through a spelling misstep used another word which happens to be spelled correctly, that is a grammar mistake my friend.
Take this example; We passed a truck the other day and snapped this photo. The word used is breath, but the correct word is breathe. This is not a spelling mistake, this is a grammar mistake.
The same holds true when someone means to type “I liked the concert” but instead types “I licked the concert”. Because the word “licked” is spelled correctly, the mistake defaults to a grammar error when read by a third party. The author knows the intent and may consider it a spelling mistake, but to a reader who can only guess at the meaning based on context, it is a grammar issue.
The following example contains several spelling errors; “requied” and “experiance” and arguably “prefered”, however the plasticity of the English language is making this a weak argument.
This sign has a trick in it. The incorrectly spelled words are “cautaion” and “regreted”, but surprisingly “in convenience” is not because both words are astonishingly spelled correctly… just grammatically idiotic.
Now, the following is not a spelling mistake. It is a grammar mistake pure and simple.