I love that the author has taken the format and themes of
Bridget Jones's Diary and spliced them onto a single guy instead of a single woman. Pretty dang hilarious! You've got the general setup of a bigger story being told through the lens of someone's seemingly banal romantic woes, lots of slang and shorthand, and even the daily "counts" that open each journal entry, in this case pushups instead of Bridget's daily weigh-in and calorie count. I find this even funnier when I remember that Bridget Jones's Diary loosely follows the plot of Pride and Prejudice, and so does this story in a similar way, what with misunderstandings and eventual romantic success.
Given all that, I agree with Max e^{i pi} that the idea that the narrator's "minimal diction" would make human language
easier for the aliens to understand doesn't pass the sniff test. In fact, the truncated language of this journal would make things much, much harder to understand even for another human who didn't speak English. In shortening the sentences, crucial information gets left out. We easily fill in the gaps because of our experience as English-speakers, but the "correct" information is not so easily supplied if you don't start with our vast amount of experience.
This is best understood with an example. Take the sentence, "Still the laughing stock of the ship". This sentence eliminates both the subject (I) and the verb [am]. For an alien, how does that make this sentence easier to understand? The missing subject and verb could be anything, if you don't know anything about human behavior in general, much less English idiom. The subject could be I, you, he, she, or they (and this is only thinking grammatically). While to us it's obvious the verb should be a "to be" verb, that's not necessarily an assumption an alien, or even a non-English speaker, could safely make without a greater understanding of the language. While we moan and groan about grammar as kids, and sometimes joke as adults that we don't need it, internally consistent application of grammar makes things less ambiguous and easier to understand, not harder, particularly for second language learners. (Please note I'm talking about grammar in the linguistic sense, not what we consider "proper" English grammar in particular. Dialects also have internally consistent grammar.)
All that aside, since this story was clearly supposed to be absurd, I'm willing to give the plausibility factor a pass. It's supposed to be a joke that a moron makes first contact because of, and not in spite of, his annoying journal. For me, the joke worked, especially given it's a Bridget Jones rom-com send-up.