What really happens in a reaction like this is that there is a large excess of acid, and any H2O that is formed is quickly protonated to give H3O+. H3O+ is not a good nucleophile, so the reaction stops there.

CH3CH2Br *will* react with H2O to give CH3CH2OH, but it is fairly slow and tends to require heat.

You’ve seen this before, if you think about it. Take water, H2O. Water can act as a base (donating its lone pair of electrons) and also it can act as an acid (donating H+ to give HO-, if you think of it as a Bronsted acid, or accepting a pair of electrons on the H if you think of it as a Lewis acid )

I also want to ask if the first step of the mechanism for that reaction is Lewis acid-base because a covalent bond is initially formed between the chlorine atom and the silver ion. I’m asking this because I think that ordinarily when silver and chloride ions bond ionically to form silver chloride it is not considered lewis acid-base because an electron pair hasn’t been transferred to form a covalent bond. In this case, however, am I right in thinking that the chlorine is part of a bigger molecule and so the bond it forms is covalent and hence that step can be considered Lewis acid-base?

Protonation will be quick, relative to loss of leaving group. The rate limiting step is still first order.