It may be the name he provided as his legal name when applying for visa/permit. Patronymic name is foreign concept for US/Canadian legal system so for immigration purposes it is treated as middle name AFAIK and quite liberally at that.

Canadian immigration service, for one, just cuts patronymic name if total length of first + patronymic + last names exceeds certain limit (my guess - the limi tis length of the field in some form/database). So "Igorevich" becomes "Igore" or "Igorev" depending on you first/last names lengths. US may have more flexible rules and lets you provide your version of middle name or drop it altogether.

I wouldn't attach too much importance to this detail

Russian user here. Yes, that's weird. I would expect something like Maxim Igorevich Popov.

Name from the article would sound like Maxim Igorovich Popov.

Vladimirovich is not a second name, it's patronymic (name of his father)