Anonymous sources indicate that the ECB's decision to hike by 50 bps was made because the SNB decided to support Credit Suisse bank. A collapse of Credit Suisse could shake financial stability in Europe, which in turn would not be good news for the ECB, which is struggling with high inflation.
Anonymous sources also indicate that only a 50bp hike and leaving interest rates unchanged were discussed. The same source doesn't say whether a smaller hike was discussed. Meanwhile, US indices are accelerating. The US100 is already testing the vicinity of 12650 points.
Source: xStation5