I m not an economist, so i might've understood your point wrong, but you just argued that the Feds offered to purchase your long term bonds for a higher price - logically this must mean you've made some money (ala, profit).
So having made profit, wouldn't you then spend that profit on something that you otherwise wouldn't have afford to spend? Thus, this introduces more spending power, and thus, introduce the inflation that you said wouldn't happen?
Let me clarify what I wrote: you have a choice between (a) just keeping the money, (b) buying some other kind of asset, and (c) spending the money in the real economy.
Asset prices can indeed go up, because people do (b), but (c) is almost non-existent, which is why these Fed operations are neither going to help the real economy nor create inflation there.
Keep in mind that those transactions are mostly done by insurances, pension funds, and other types of "money managers".
So having made profit, wouldn't you then spend that profit on something that you otherwise wouldn't have afford to spend? Thus, this introduces more spending power, and thus, introduce the inflation that you said wouldn't happen?