It's good advice. Taking on a sword with just a knife is really, really, really hard. If you're not superhuman, probably can't be done against a halfway skilled opponent. I've seen video of people trying and they just laugh afterwards about how impossible it is. But, if you were going to have a chance, obviously it would require lightning fast closing to very short distance.
(You might think you could just parry the sword with your knife and move in, but swords don't stay parried. One of the core things in sword fighting is, what to do after your swords make contact, and that includes things like controlling the other person's blade so you can hit them anyway, and disengaging your sword from theirs so you can whip it somewhere else and hit them. So you better do that "move in" so fast it's faster than they can twitch their forearm)