It's Okay To Say No
You're sat on an empty bus and someone sits next to you and starts chatting to you. How do you feel? Do you move? Feel uncomfortable? Do you feel annoyed? Do you enjoy it? You have a choice here, you can easily move away, you aren't stuck in that situation.
Think about this: You're in quiet park and your puppy is happily playing off lead then another dog runs up to your dog, trying to play. This may look good because your puppy is 'socialising' and enjoying themselves. BUT are they really enjoying themselves? Are they actually trying to escape from the other dog? Do your dog a favour and learn to read them. Learn what their body language is telling you.
Not all puppies are sociable, just like us. Give your puppy choice to not have to play or stop and say hi to other dogs. It's okay to say no. Our job is to make our dogs feel safe and 'forcing' them into situations can really have long term effects. If in doubt then get your puppy out of an experience that you don't think is good for them.