People with HIV are more prone to meningitis:
https://www.google.com/search?q=hiv+meningitis
Approximately 1 in 10 are “carriers” of the bacteria:
https://www.cdc.gov/meningococcal/about/causes-transmission.html
Seems to me there’s a reasonable chance this unfortunate young man was a carrier who had his immune system compromised by the stab. The leftovers may have had nothing to do with it, or could have been a trigger because he had weakened immunity.
Now that’s an interesting thought.