As Tom said, the man has "two time release capsules on his back" then the scene changes to show one. But before they pointed that out, he started with one.

Is that Desmond Llewelyn who throws the switch when they try to electrify Mama Gorgo? I know he isn't listed in the credits, but so few people are....

So that's what Q did, before he worked with Bond!

If it was him, it's not in his IMDB profile.

According to his Wikipedia page, it was him.

Well neither source is entirely infallible, so who knows.

Actors often did that when they're starting out. Take uncredited roles.