I found it somewhat amusing, and whilst it did not have a significant effect on my understanding of the article it did break 'the flow' and made the piece much less compelling.
Does this hurt the authors credibility? Yes.
The piece is a summarisation of a book literally called "On Writing Well" yet the text itself shows the author has not fully digested the information they are regurgitating. This is ironic.
That said, it is very well written for a non-native speaker. I would feel much more comfortable having this author communicate on my behalf than many native English speakers that I am close to. With some practice (probably including spoken word and works of fiction) there is no reason they could not exceed the skills of the majority.
Does this hurt the authors credibility? Yes.
The piece is a summarisation of a book literally called "On Writing Well" yet the text itself shows the author has not fully digested the information they are regurgitating. This is ironic.
That said, it is very well written for a non-native speaker. I would feel much more comfortable having this author communicate on my behalf than many native English speakers that I am close to. With some practice (probably including spoken word and works of fiction) there is no reason they could not exceed the skills of the majority.