Growls can mean a lot of different things depending on the situation. Some breeds are more vocal than others and more likely to growl in certain situations (ex: play growling). Sometimes they are a playful noise- that is called a play growl. Sometimes they might mean "I am uncomfortable with what is happening". Sometimes they mean "I am uncomfortable with what is happening and might/will bite you if you keep pushing me".
Bostons are one of those breeds that do tend to be more growly. They might growl when they play, when they want attention, when they're a little bit uncomfortable, or when they are really uncomfortable and may defend themselves.
Generally, dogs do not like to be picked up. At 10 weeks, it is unlikely that this growl is an actual threat in the sense that this puppy is going to follow it up with a bite, because 10 week old puppies tend not actually be aggressive, even in situations where in adult dog might be.
My guess is it is either the dog thinking you're play or, more likely, the dog protesting being scooped off the ground and held feet in the air against its will.
With small breed puppies, I always suggest desensitizing them to being held and avoiding carting them around unless absolutely necessary. If a dog is comfortable with being held, I may take them places for socialization before they are fully vaccinated (because they can't be walking on the ground yet), but once they have all their shots I prefer to keep them walking on the floor whenever possible.
I have a Boston who is a little over a year old, and it was very important she be comfortable being held because I lived in NYC during her first year and needed to take her on the subway a lot, which required me to be holding her. With picking a puppy up, if the puppy is growling at being picked up, start giving him a treat before you pick him up and after you pick him up, and giving him treats randomly when you're holding him. I would use something like cheese, pepperoni, pieces of deli meat, chicken, or hot dog, that is super exciting. This is what I did with her, and everyone is always surprised at how calm she is about being picked up and held.
Ideally, if a dog is uncomfortable being picked up, you aren't forcing them into it and doing it only when you absolutely HAVE to. IMO, its totally understandable for a dog not to like- I wouldn't like being picked up by a giant.
I wouldn't say it means there's going to be problems in the future, though it might point to a dog that is going to have some trouble with being held/restrained physically/touched in certain places as an adult. Really though, I don't think its too crazy for a puppy to let out a small growl when being picked up and it isn't something I would worry about too much, just make being picked up become less upsetting for the dog by him always getting a treat after it, avoiding dong it excessively, and making sure he is being picked up in a way that makes him feel more supported (ie, don't be picking him up under his armpits, scoop him up so his belly is being supported).