If someone used the phrase quite concerning

[Loveandpeace56]

Would you take this to mean this was a big deal to the person?

I would use it in that way yes

Quite concerning = very worrying.

Generally yes.

I mean it does really depend on the context and tone surely? In a serious way about a matter of gravitas I would use it as, and take it to mean that something has been flagged that seems like a problem but that might not necessarily mean it ends up being THAT bad, just a bit of a worry.

Doctor saying it about a family member’s illness. Very worrying.
Precious girlfriend saying it about the au pair asking to leave half an hour early to catch a flight home on Christmas Eve, not so much.
Generally ‘quite concerning’ is a giant klaxon alerting to you to be prepared for if not the worst, the something very close to it.