Typically it's for Mg def. I don't see that in your plant. It also has sulfur, maybe he's recommending it for that.Is the epsom salt just for the perkiness?
It looks like overwatering. Soil ph rises as it dries. If it's kept too wet, it could limit the availability of N at higher ph.
I would put 40% perlite in that soil next time. It looks too dense/heavy. (I like perlite. Lots of it.).