It's just one of the idiosyncracies of the .win network.
If you come here through KiA2's own URL, https://kotakuinaction2.win/, and you click a user profile to check a user's posts, you only see posts on KiA2. If you use https://communities.win/c/KotakuInAction2/ and do the same, you see the user's post history on all communities. I'm guessing /uBidenLikesMiners uses the former, so he thought you only two posts total.
Are you confused? I've only had an account on .win for about 2 weeks and I've commented in other communities...
It's just one of the idiosyncracies of the .win network.
If you come here through KiA2's own URL, https://kotakuinaction2.win/, and you click a user profile to check a user's posts, you only see posts on KiA2. If you use https://communities.win/c/KotakuInAction2/ and do the same, you see the user's post history on all communities. I'm guessing /uBidenLikesMiners uses the former, so he thought you only two posts total.