I personally find bidens response deliberate, and intriguing.

He made no explanations, and was very short and said "no".

And that could sometimes means he is deliberately answering the specific question precisely.

Iow, it could be possible the US is sending new f-16 to Poland and Poland is sending old ones to Ukraine, for example. I'm not saying that I think this is happening, but sometimes precise short answers can be for reasons like that.