I sometimes hear "We have so much technical debt! We're using Mongo when we really should be using Postgres for this data structure."
Not technical debt, just a preference for doing things a different way (which admittedly might be a better way, but just because there's a better way doesn't mean the current way is bad)
Sure it's debt if the choice to use mongo causes the bad decision to seep out into other parts of the codebase.