They were literally buying US government bonds based on outlook given by THE government agency which gives OUTLOOKS & sets POLICIES on these matters.
They literally did the you are "supposed" to do and they were called "greedy capitalists" or chumps for not doing sophisticated active player stuff like hedging.
But were they irresponsible? Not really. This is a scenario that's very easy to see the flaws of in hindsight.
It was a huge gamble.
Was it a "huge gamble"? NO! Banks are literally in the business of long duration.
The Feds were draining liquidity at the fastest rate in recent history and they did this right after an extremely over leveraged bull run leaving the entire system very fragile.
A collapse was inevitable, SVB just happened to get the short end of the stick and yes they put themselves in that position through incompetence/arrogance.
If not SVB, it could've been maybe a bank over exposed to the commercial real-estate market or literally any other area left too fragile.