As an ATCO I work as part of a team although when in position I have a specific area of responsibility.
Similar scenarios to the one in this thread occur where a controller (or ATSA) working an adjacent sector may notice a possible "situation" but is 99% per cent sure you are dealing with it but for comforts sake will say "have you turned XXX" or "He's still descending" - you get the idea (I hope). We may feel awkward about possibly overstepping a boundary and annoying our colleague/s when they have the situation fully in hand but what happens when there was a genuine oversight (yes - we're all human)? Even if risking an irritated rebuke, for safety's sake - say something! - it saves having to deal with the subsequent board of enquiry. I would hope that the ATCO concerned later thought about what had occurred and realised that your reaction on the R/t was not a slight - merely concern.
It's always better and safer to check than sit fat dumb and happy until the accident happens! We're all human!