I believe the intended point is that one may say that two statements have the same or similar meaning, but without using a mathematical operator such as the "equals" sign. For instance, one could say that "Obama was elected in 2008 and again in 2012" is a true statement, and that another way of saying this might be "Obama was a two-term president". But it would be nonsensical to say "Obama was elected in 2008 and again in 2012 = Obama was a two-term president".
The statement is an encouragement to use mathematical notation, and English, in proper ways. The "equals" sign should be used between two expressions which are mathematically equal, not thrown in, willy-nilly, any time two items are related, or merely because one might logically follow from the other.