It 'can' be a typo. One of the essences of spelling is kinaesthetic memory, where you think a word and your brain starts your muscles writing it without any further input. In other words, it's automated spelling once you've thought the word (which is why it is so very difficult to correct a wrong spelling that's been engrained over time).
I don't do it when I'm handwriting, but strangely, when I'm doing my hunt and peck keyboarding, I sometimes get a time when my brain says 'I know that one' and gaily tells my fingers to write 'are' instead of 'our', 'their' instead of 'there' and 'your' instead of 'you're' etc.?.. It's bizarre, because I've always been an excellent speller. But I can generally spot it immediately if I proof read.
So I do cut people a bit of slack when they're typing rather than hand writing. ?
But it annoys me hugely when people do it all the time