As other posters have said, it does depend entirely on context and manner.
So if there is something up on the board, but I am explaining / talking about something else, and Child A (who has clearly been paying no attention to the lesson) says 'Miiiiiiiis, there's a wrong spelling on the board', then I might be less than impressed, because they haven't been listening.
if on the other hand I have made a spelling mistake while e.g. modelling onto the board, and a child points this out in a timely and appropriate way (it is surprisingly easy to mis-spell when writing quickly on the board), then I just thank them for pointing it out, correct it and we move on.
However, I am a reasonably confident teacher, and in general a decent speller, so I do not get bothered about someone picking up the occasional error, if they do so politely and at the appropriate time. If I was not a confident speller, and felt uncomfortable / more vulnerable in this area, it might be harder to shrug it off, if that makes sense? It's not an excuse in any way - the good teachers I know who are relatively poor spellers are very aware of it and work very hard at it, the poor teachers who are poor spellers perhaps less so - but teachers are human...
I do also think that the question about the tone of voice / manners that a child might be hearing at home is VERY relevant, though. Put it this way, I do very often sit in parents' evening and think 'Ah yes, that's why my pupil speaks / behaves in the classroom as they do', because the way that the parent speaks to me or their partner is very similar. If a child hears adults in their life talking to one another politely and with respect, they will tend to echo that in their own dealings with adults. If they do hear one adult being snide or sarcastic or aggressive or condescending to another on a regular basis, then they are likely to produce an echo of that tone themselves - and perhaps be less sensitive to how it might sound, because to them it would be 'normal'.