This is a false positive.
Whenever you want check something like this, also check a known innocuous file. I exported a png from photoshop consisting of a single magenta fill. Using malwr, I scanned it and got the same two signature matches: https://malwr.com/analysis/ZGUwZjcwYzY2YTZmNDk3MWFhOTEwNmM2NmQ5NGVhNGU/
Note that these are SIGNATURE matches. Clearly something is triggering this, but I'm not sure what. No part of those values shown under "signs" actually appear in the files.
Note that none of the strawmen files that I've seen(including the large jpg mentioned) actually contain "strings that are used in other pieces of malware."
Edit-before-I-even-posted:
I created a file, filled it with ascii gibberish, named it gibberish.exe and uploaded it to malwr. Here's the full contents of the gibberish file:
fasfaf;sdfkh'hdignipasgiasdgipasdghighighighivmse[pm8uvtopawr8tvo;srm,
here's the scan result:
https://malwr.com/analysis/Mzk5N2NjODQ5MDhkNGM1ZTk4YzkxNzEwNjJlM2MzM2Y/
Either their virtual machine used for scanning has a virus on it, or their software is misconfigured.