I don’t think I get it, the conclusion doesn’t make any sense to me at all

Because yes, there is an infinite amount of infinities when you think of decimals. We have two when it comes to integers - negative infinity and positive infinity, and there is an infinite amount of infinities between any two integers. 0 - 1, but also between decimals 0.1-0.2, etc

That doesn’t mean you can’t add or multiply any two numbers just because there is an infinity inbetween.