I too was having a hard time understanding why a bank would want to shoot itself in the foot (from a traditional banking point of view) until I read this:
It's not uncommon for Volksbanken Raiffeisenbanken / Sparkasse in Germany because their business model is indeed very decentralized. It's called Genossenschaftsbank in Germany, somehow comparable to Cooperative banking. And in Germany, there are many partially independant, local branches (like for that Example Bayern Mitte (middle Bavaria)) and such banks are very customer friendly.
By selling / converting BTC, the bank would still make a profit and the article also mentions to sell education-courses for customers interested in Bitcoin (most likely inlcuding informational material).
Apart from that:
This can cause a chain reaction. Banks from other countries will also join this game in order to keep up with pioneers like German bank. That's when the fun begins when other bank start making such statements at the distillation.
What you say is very unlikely. What we are seeing here is the exception and not the norm. This is a special kind of bank, but big banking if it adopts Bitcoin is going to be to offer custodial services, Bitcoin-backed loans, etc. Precisely the Bitcoin originated against big banking, who, in addition to central banks, can also create money out of thin air thanks to the fractional reserve system.