There must be a whole back story there, but I've decided not to go poking around for it. Most celebrants focus on weddings, although funerals are in the mix as well. I've heard of baby naming or child welcoming ceremonies as well. While in theory a baptism is entirely possible, I've just never actually heard of a ULC minister performing one. My guess here is that a family wanted to have a christening for their child (or children?) without involving a church. Someone who isn't affiliated with a parish might find it difficult to obtain such a sacrament without either having to feign participation for a while beforehand, going through some preparation with a clergy person, or both.
As a Humanist celebrant I certainly won't be doing any christening or baptizing, but the aforementioned baby naming or child welcoming options exist. If you're interested in that or need someone to officiate your wedding in New Jersey, contact me.
Update (08/20/2022)
Here's what the ULC minister above offers as baptism.