Meldrum wrote about a personal encounter in his Legend Meets Science book. In 1997 he had a non-visual encounter in Northern California involving something coming into his camp at night and leaving large footprints. I didn't get the impression that this experience converted him into a knower but it probably nudged him in that direction. Standing may have tipped him over the edge.
I'm ambivalent on Standing. I remember watching his Discovering Bigfoot documentary and thinking he seemed to push Meldrum into supporting Standing's claim of being the Jane Goodall of Bigfoot. Standing would keep encouraging Meldrum to do things to deepen his commitment, such as put an apple in a tree, do a Bigfoot call, confirm a foot impression is a Bigfoot print, or admit that he saw that shadow and it was a Bigfoot. It all seemed suspicious to me.
A couple months ago I wrote about the anatomy of a hoax, and honestly I think Standing's behavior shows a similar pattern to Hansen's regarding the Minnesota Iceman, and unfortunately I think he may have been using Meldrum's desire to believe in Bigfoot as a pathway to convert Meldrum into a champion for Standing in the Bigfoot community. As @Huntster says, though, this is all conjecture.
Here's my post for those interested. I'm not above a little self-promotion. https://thesocialbigfoot.substack.com/p/the-art-of-the-hoax