Since data science and text analysis has blown up recently ( this decade ), Plagiraism checkers have been a huge use for it.
Problem is, text analysis can range from the very rudimentary (check how many times a word appears in a document and come up with a ratio of it to the all the words in the document) to the very complex (look for sentence structures, topic analysis, etc).
You would think that journals would run some high-end plagiraism checker, but you never know. They may be running a rudimentary checker that just racks up all the words in your paper and it seems to pattern-match the ratio of words you use compared to your whole document to seem similar enough to another person's document. But, that wouldn't take into account the order in which the words are used.
I would ask them what analysis software they're using. Seeing as it's a journal, and science is all about reproducability, they should be able to direct you to the plagiraism checker to let you run it through yourself and see what it's doing and also provide in-depth knowledge of HOW it's doing it.
Because the biggest concern in data science (and all it's applications .. including text analysis, ai, machine learning) .. is you want to know how the inner workings of something work. That way you're not at the mercy of some "black box" spitting out some answer that everyone is taking at face value (when there could be HUGE amounts of bias or overly-simplified stupidity going on INSIDE the black box).
I would also worry about anyone you may have shared your work with.. even in confidence.
I worked with a group one time where we shared our work internally. But, one guy in the group was friends with some folks in another group. They were having issues with something, so they asked him for help. Like most folks, he was lazy, so instead of walking through everything with them.. he just showed them our work.
Later on professor was asking several groups to step forward to figure out who did original work and who plagiaraized. Because what this one group was doing was asking ALL the groups in class if they could "help" them with different parts.. then just stitching everyone's work together and submitting it as their own.
The guy in our group did not say he was showing our work to anyone. I operate in a group environment under the unspoken assumption that it's just common courtesy to not show a group's work to any outside parties unless you get the inner-group's permission first. So, I was floored that this guy was sharing our work w/o our knowledge.. and it had vast repercussions. (Because at the school I go to, the honor code states that the folks who got plagiarized are just as responsible for the folks that plagiarized.)
So, I would think about who you possibly showed your work to. You may have thought you showed it to them in confidence, but they could be wandering around showing others.
And if you did this work for a class.. a professor may have taken your work and turned it in as their own. That's not uncommon.
This semester a professor is letting another prof show up and toss a mini data science project onto us. I've had this other prof before, and he's the type that asks students to do in-depth research projects in his field of interest, and there were rumors of him just turning around and publishing their work as his own after he fleshed things out a bit more. Well, the project he's tossing on us is another one of these "I have no clue how to do this, so I task you with dreaming up a way.. oh, and document and detail everything as if it's a research paper." I find it very shady.. and assume he's just going to take everyone's work, condense it down, and publish it under his own name after-the-fact.
So... think about who may have had access to your work. There's some underhanded, shady folks out there.