Greeting and barking - bad behavior??

Chiquito met 4 of his fur cousins at our house today. There were also 20 hoomans (big and small) here. It was the first time we have had a largeish get together at the house with him, and it is the first time he has ever met a dog in his house.

Overall I am pretty proud of the way he behaved - managed a sit the first time he was asked 99% of the time, held a wait command almost perfectly every time it was given (including while all of the dogs were getting/sharing treats) and after the initial psycho greeting moment (on lead) he managed to not jump up on anyone (including the wee little people) for a pat too often either

There were two behaviours that I noticed and am a little unsure of though:

1. When he met the dogs (on lead) he went up to them, said 'hi' to their face and had a good bottom sniff, but when they went to return the favour he would move to 'avoid' this ... almost like he was scared (bottom end down toward the ground)?
2. The second is that, after spending time saying hello he would then start to jump toward and bark at the dogs 'asking them to play' (bark with that funny crowing sound, tail wagging, ears up). This happened both on and off lead and taking him for a walk around the block, reminding him to calm down, giving him time out and using treats to try to stop this had no effect at all. Two of the dogs did tell him off for this which calmed him down for some time, but he did start again later.

My questions are - The barking is new; is it possible he has learnt it from the puppy at preschool that does this or is it just something he is doing because he wants to play? Are it and the no bottom sniffing rule poor behaviours? Is there anything I can do to correct the behaviours, or should I not be correcting them?

(If you made it to here you are a legend - thank you!!)

He could've picked it up. When we went to puppy classes, the trainers told us every time a dog barks, all the dogs except that one get a treat. That way they learn if they stay quiet, they get a treat. It helped, because Loki never barks at other dogs, even when he wants to play. The jumping about is him not knowing manners, so if he's getting too rude and excitable, I'd move him away for a little while to calm down, so he learns to play nice. Took Loki months...MONTHS...mind you but Chiquito sounds like a very fast learner to already be doing so well

Thanks for reading my novel Tara -appreciated

Thanks for the advice - I figured the jumping/barking was a play behaviour but was not sure what to do. Can I ask, with Loki did you meet on lead? And did you reward for the calm behaviour when you walked away?

(PS .. We've been practicing the devil out of on sit, wait and no jumping while at home, on walks and at puppy preschool for the last five weeks - I'm glad he got it yesterday, but it definitely isn't a every time thing yet )

Yeah, Loki always meets new dogs on-lead, for the simple fact that he's always very excitable and it can annoy some dogs. He's better now, but for still want him to meet dogs on the lead so I can move him away if need be. I don't reward him for his good behaviour anymore because it's normal for him now, but at the time, he was rewarding for being calm or polite