I can think of at least one reasonable possible explanation for BL’s parent’s behavior that doesn’t mean they have an utter disregard for GP’s family.
This is speculation only and NOT necessarily what I think happened. But it could have.
Let’s say BL arrives home, telling his parents he and GP broke up. He says they had a big fight, decided to end the relationship and the trip, and agreed he would drive back to Florida alone (because the van had to get back east somehow, it would be safer for BL to drive alone cross-country than GP, GP didn’t really like driving the van, and neither wanted to drive cross-country together). Possibly BL told his parents that GP had become friends with some other vanlife folks at the campground who offered to take her to the airport to return to NY, or maybe he told them that GP was planning to travel with her new friends for a few months and continue working on her vlog.
Maybe BL told his parents that he and GP decided to deal with getting the van and her belongings back to NY in a couple months, when they are both in a better place emotionally (or when GP returns from her travels).
Maybe BL’s parents know GP as a friendly free-spirit who works really hard at whatever she puts her mind to and as someone who makes good decisions. Her decision to fly home on her own or possibly continue on without BL, and his return home by himself with the van, could make sense.
Perhaps they had seen unhealthy interactions between GP and BL before, so were actually pleased the relationship was over.
If BL had no history of lying to his parents, they would have had no reason not to believe him if he arrived home with a reasonable-ish sounding story. If he was a “good kid” growing up, he might have earned the benefit of the doubt even if the story sounded a little off.
Let’s say BL also told his parents that GP was calling him over and over on his way home, wanting to talk about getting back together. He tells them he kept asking her to please leave him alone and give him space, but she wouldn’t stop calling, so he eventually blocked her number. He asks his parents not to answer if she calls them or tries to get in touch with him using their numbers.
BL’s parents, believing BL has just gone through a difficult break-up, try to distract him and keep his spirits up by doing fun things and giving him space to grieve.
After a while, BL’s parents get a call from GP’s parents. It’s reasonable to think they might tell BL, “That’s weird, GP’s parent is calling me.” I can imagine-
1) BL saying “Sorry she’s harassing you guys now too; I’ll deal with this,” taking the phone to another room, listening to and erasing the message, and possibly blocking GP’s parents numbers on his parent’s phone, or
2) BL saying “I’m sure it’s GP trying to get me to talk to her since I blocked her number, please don’t answer.” When BL’s parent sees that a message has been left on the phone, they give the phone to BL, thinking the message is probably from GP and not wanting to listen to a private message.
Either way, BL listens to the message and hears that GP’s parents are going to call the police. He deletes the message, tells his parents it was more pleasing from GP, and asks them to please block all numbers associated with her for a while. He makes plans to leave the next day and never tells his parents a thing.