As always, it’s almost better to ignore the pictures when possible. This gentleman has a peptic ulcer, which we know is caused predominately by H. pylori infection. H. pylori produces proteases and particularly urease, which allow it to increase the pH of its local environment by cleaving urea into ammonia, which is toxic to gastric mucosa. The picture demonstrates H pylori, which are evident with silver staining.
but what is wrong with "Spirochete invasion of gastric cells"? It seems like H pylori is sometimes described as curved and sometimes as a spirochete. And "gastric cells" is general enough that I don't see why it can be wrong. There is H pylori in the gastric cells.