Sounds hoakey to me.
Chrysler doesn’t make their own spark plugs, in fact I think they are made by Champion. Most of the time mechanics like to keep with parts they get from the dealer because a) warranty and fitment can be assured and b) they don’t want to take the time and/or be responsible for researching an alternative that may be as good or even better (or cheaper).
IMO, there is no reason to buy parts from the dealer if they can be purchased somewhere else. There are always parts that will work that are sometimes cheaper, sometimes better and sometimes both, you just have to do your homework.