By the very act of presenting something like that to the larger community you are engaging in a competitive act.
No you are not. There are multiple reasons why you would want to present something to a larger community, only one of which is competitiveness. Simple things such as having peers review it, suggestions, receive praise for doing something, getting upvotes, and more could all be a reason for posting something to a larger audience. I'm sure there are things i've not mentioned.
Source for what? A baseline for claims to achievement are why anyone cares about such distinctions at all. Just ask folk which mods, if Wube were to allow some mods to not disable steam achievements, should qualify.
Steam achievements are not the same as posting on reddit for others to view. I could