In high-level diagrams, which I think is what is being discussed here, I like to think that A --> B means that A "uses" B in some way, and leave it at that.
The database can live without the web server, but the web server doesn't work without the database.
Therefore webserver ---> database.
Key thing in that these deployment / context / container diagrams don't have a temporal axis. If you want to represent a flow, then you want a diagram where time has directionality, like a sequence diagram.
A > B > C
Basically you're leaving it vague because you can't be arsed to actually work out what it means, and every reader is invited to come up with their own individual wrong assumptions and misunderstandings.