If I recall aright, they traded off in that one; Bixby was made up to resemble Ferrigno for closeups, and Ferrigno was made up to resemble Bixby for shots where the character had to move around and be bulky. They did a fair bit of fancy editing to maintain the illusion, or at least that was the intent.
I also recall that episode as a two-parter. Banner/Hulk encounters a blind woman living alone in the woods, just like that one hermit from Bride of Frankenstein. It’s real poignant. Instead of burning her cottage down by accident, Banner/Hulk beats up her toaster when he sees his reflection in it and becomes enraged. But he hastily apologizes for it, so it’s cool. That was an interesting bit that stuck in my young consciousness, cramped in there alongside plot contrivances from Gilligan’s Island. “Interesting! So if the Hulk could talk the rest of the time, chances are that he’d apologize after he breaks things. That’s good to know.”
Then the military tracks down the meteorite impact site and mistakes the Hulk for a space alien. They conveniently happen to have a giant metal dome on hand that they lower down from a helicopter to capture him. This was the point where the series’ credibility problems started to become apparent to me.
Also, the meteorite resembled a giant potato.
