This doesn't surprise me at all. Consider that the US has a federal agency set up specifically to pay out vaccination harm claims, and intentionally sets a low bar for those payouts. The rationale is that getting lots and lots of people vaccinated is a public good, so it's best to reassure people that if something bad happens that seems to be even vaguely correlated with a vaccine they take, they'll be taken care of financially.

Certainly this particular vaccine situation is unique, but indemnifying AstraZeneca, especially after asking them to sell the vaccine at cost, doesn't seem unreasonable.