Stunkladha

First, general body structure: The ghast is primarily composed of a single cube with tentacles below it. It's face is on the front of it's body, with two eyes and a mouth and no visible nostrils. The strider is composed of a single cube with two legs below it. It's face is on the front of it's body, with two eyes and a mouth and no visible nostrils.

Let's also add that the strider's concept art has it resembling the ghast even stronger than it does currently with multiple legs and much larger size. Even if the final design doesn't seem super ghast-y to you, it definitely started at a point where it was related to it.

Also you might've noticed that the strider concepts actually show some lines on the sides of their head... But is that in the final version of the strider or...

Oh wow, they are!! When we remove their "bristles", we can see these lines on the sides of their heads. Hey, what else has lines like- yeah, it's the ghast, what did you expect. They also have similar lines on the top of their head, which are shown better through the back of the strider where they continue down... just like the ghast has.

I could also mention somber expression, but that doesn't feel as concrete. I can look sad and not be related to the ghast just fine. However, as a design choice to reference each other? I could see it being a thing.

But one thing I do want to mention is how their immunity and seeming love for lava. The strider's connection to lava should be obvious, as it's part of their purpose. Striders get visibly distraught and discolored when they leave lava, so their love for it should be obvious.

But the ghast...? Well, nothing concrete, given that they're an old mob and have generally random behavior, but I do think that ghasts are supposed to like lava in-universe. For one, the Mob Menagerie on them says that "they love the warmth of lava". This is a recontextualization of how sometimes Ghast can get stuck in the lava falls of the nether.

Source: Mob Menagerie: Ghast

Also, when the upcoming summer drop is eventually released, Ghasts will have a variant that can be given a harness, which is a version of a saddle specifically made for their size. Hmmmm, what else can be saddled and ridden....?

Yeah I know, not a crazy argument for this, but considering this is one of the first ghast updates in a while and it's main thing is adding rideable ghasts. Previously, the only rideable nether mob was the strider, so this feels somewhat significant to me.