Hi Jacqueline, well for a start off you have a beautiful name, its my sisters too and I always wished it was mine!
I think you handled the situation well, holding him till he calmed and obviosly it was the right thing at the time as it resulted in cuddles afterwards. When kids flip out they need to be held to feel secure. Well done for calming him.
Kids lash out at the people they trust and love, I don't know what caused it but its out now, he's had his outburst, seen that you'll both be there for him and I'm sure his angry words were just part of the tantrum and not meant in any way at all.
Its always better for them to get it out of there system, no a tantrum in a 5 yr old isn't what we hope for but if he had so much building up inside him its good that he let it out. Hopefully today he will feel calmer and you can talk to him about things before it builds up to that point again.
Try talking to him about his feelings, if he's not able to say what he felt try asking what colour he felt, I use that with my kids sometimes, its easier for them to say a colour that describes there emontions sometimes when they can't find the right words. If he does flip again, do just what you did this time, let him know that however angry he his you're there for him, you won't let him deal with it alone, it will make him feel safe. Talk to him about what he might do next time he feels so cross, give him a signal he can give you to show you he is feeling angry again so you can sit down with him and deal with it in a better way.
I wouldn't put it all down to your new partner, there may be other things going on in his head, he may be angry that his dad's not living with him anymore, troubles at school or with freinds, sometimes its a lot of little things that overload the brain to cause big outbursts.
I'm sure you and your partner are wonderful parents, you didn't flip yourselfs, you did what needed doing to calm him and where there for him when he needed you most. Don't take what he said to heart.