"They" is a gender neutral pronoun, used out of respect when you don't know the gender pronoun someone goes by, and don't wish to be presumptive.
What about my comment made you think telling me to 'calm down' was warranted?
However, it is even more acceptable to refer to someone by their name, in this case Gustave Eiffel, instead of only using pronouns. Furthermore, "the architect" can be used, since it singularly denotes a specific person. There are many constructions that are better than using the imprecise "they".
Does it matter? Sometimes you want an imprecise "they".