I've experienced the sensation for as long as I can remember. I'm in the cohort that got hooked on the feeling watching Bob Ross in the 80s and 90s.
I will occasionally have chills or goosebumps in response to great music or to a particularly emotional scene in a movie. For me, this is an entirely unrelated phenomenon, and the sensation is distinct. My ASMR triggers really don't involve an emotional component. In fact, I would say that I am in more of an analytical and intensely focused frame of mind when I experience ASMR tingles. I think a pretty common aspect of most ASMR performances is a pleasant, but flat affect. Gut-wrenching does not make for good ASMR.
My favorite video trigger is watching a skillful origami artist fold a complicated model. Hands only, no talking. There is an element of closeness or intimacy as it appears as though I'm watching from very near the artist. There is the element of precise and purposeful movements. There is also a quality to my favorite triggers that doesn't get mentioned often (but it does come up occasionally), and that is an element of anticipation and surprise; that it's not entirely clear what the actor is going to do next, but it's clear that they know exactly what they are doing.
That last element relates to another common trigger for me. I will often have an ASMR sensation when I am listening to a great storyteller. It was also pretty common to have the sensation in college lectures presented by very engaging professors. Another good IRL trigger for me is learning a new lab technique or surgical procedure from an experienced researcher.
I do believe that the grooming behavior theory is a good one (i do get some tingles when someone, for instance, runs their fingers through my hair.), but I don't think it describes most of the situations that give me tingles. Most of my triggers involve some closeness or personal contact, intense focus, and learning or acquisition of an (arcane) skill, or a nugget of unusual or unexpected information.
From browsing through ASMR videos on you tube, I think my experience of ASMR is not unique, but triggers are definitely not universal. For some people it seems to be almost entirely aural, for some it's more physically sensual (but not often sexual), for many, including myself, triggers are much stronger when there is an intellectual component as well. That suggests to me that in addition to the grooming-partner bonding instinct it might also have something to do with an instinct for mentor/student bonding.