If it's real, it's either: 'l' and '1' were written in a homogenous way for the majority of users to mistook the characters or it's actually an eye checkup for prescription glasses.
Any source of that 'interview' so we can "evaluate" its magnitude?
Responding to your questions, the source of those interviews with users is me.
It would be incredibly unlikely when reading from a screen, since most fonts quite clearly differentiation between lowercase l and the number 1. It would be very possible when reading from something hand written, since many people write these the number 1 simply as a vertical line.
There are contridctory findings in many comprehensive, widely-known researches. As a matter of fact, it is very likely that letter l is mistaken as numeral 1 when reading both from screen and handwritten text: "To cite another example, those familiar with computer-generated passwords know how easy it is to misidentify a lower case letter “l” in a password (or email address) as the numeral “1,”" ("
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5614409/"). \
I encourage sharing own experience by all forum members.