That's the point! Using the algebra from the article:
(1 - 1 + 1 - 1 ...) = 0 + (1 - 1 + 1 - 1 ...)
and therefore:
(1 - 1 + 1 - 1 ...) = (0 + 1 - 1 + 1 - 1 ...)
And as they're mathematically the same (again, in the article's algebra), why not replace one with the other?
The problem is that when you do, and you sum the two infinite series using the "zipping" method (as in the numberphile video) the two equations equate to different results.
(1 - 1 + 1 - 1 ...) = 0 + (1 - 1 + 1 - 1 ...)
and therefore:
(1 - 1 + 1 - 1 ...) = (0 + 1 - 1 + 1 - 1 ...)
And as they're mathematically the same (again, in the article's algebra), why not replace one with the other?
The problem is that when you do, and you sum the two infinite series using the "zipping" method (as in the numberphile video) the two equations equate to different results.