Well, to me it's not a glaring red flag that would end the relationship right now, but something to be cautious of and to sit back and observe over time.

If it hasn't come up several times before that he seems overly attached, then one time alone is not really enough (imo) to conclude that he cannot have a healthy relationship with a woman.

But as my therapist says about yellow flags, they are something to watch and observe.... to be aware of and to see if a pattern develops. Where it can be unhealthy is if his attachment negatively impacts your relationship or your own mental health.

My therapist compares the feeling out period of relationships to buying a car... driving it, looking under the hood, kicking the tires, etc etc before committing to a purchase.