To me it sounds a bit contradictive in this lesson: first, you say "nouns that end in a consonant and refer to inanimate objects are generally masculine" and then you continue with "you cannot predict the gender of inanimate objects".
I have no problem with having to memorize things, but I think that first part may be confusing to some, so it might be better to just leave it out.
I'm very much enjoying the lessons in general though. ¡Gracias!