I don't think the implication was that Biden was there to discover the balloons. I don't think the POTUS has anything to do with the whole F2T of any of that.
That article wasn't posted to throw shade at Trump. It was posted because the Biden admin accused the US public of not caring when Trump let balloons fly over the US but suddenly it was a problem that he's not shooting them down over Montana. The Trump admin and the DoD later released info that said they weren't even aware the overflights were happening while Trump was in office, it didn't become apparent to the DoD until afterwards, and only upon review did they recognize this had been occurring since Trump's presidency. Now, I'm not "in the know" anymore and frankly don't care to be. But that is the public narrative and that is the narrative China is digesting--is that the US didn't recognize immediately that these overflights were happening, then when they did recognize it they tried to keep it hush from the public, and only after the public started seeing the balloons and asking questions, did the government become transparent with more info.