Solubility of sodium chromate: around 25% w/w (more precisely, 47 g of Na2CrO4·10H2O per 100 g of water). Well soluble if you ask me.
Solubility of lithium hydroxide: definitely lower, around 11% w/w (12.8 g of LiOH per 100 g of water). Still, that's 5 mol/liter, well soluble if you ask me (although it has much lower solubility than other alkali metals hydroxides).
Unless you were told what it is supposed to mean in the context of the course "slightly soluble" is a useless term, as it is not well defined and ambiguous. For me both substances are well soluble, even if LiOH definitely differs from its analogues.