In the following quotes, the word "slightest" has the indefinite article "a". Are these grammatically incorrect?
A Mother's Secret by Scarlet Wilson
"So what do you think?" He spun around in his chair until he faced her, leaning forward, his elbows on his knees, giving her a slightest glimpse of his dark curled hair at the base of his throat.
About the author; “Scarlet Wilson wrote her first story aged 8 and has never stopped.... Scarlet lives on the West Coast of Scotland...”
Ulverton by Adam Thorpe
This room grows so tedious and fusty. Because I have a slightest of fevers I am to be confined a further week upon the end of the month.
Wikipedia has an article about the author
I posted a similar question on English Language for Learners:
I've never seen a dumbest girl like this
Users said these examples were grammatically incorrect, but I am not fully convinced since the authors are native English speakers.