It would, at least in theory, be better to realistically say what we knew and didn't know about the risks.
But public communication about those kinds of risks and tradeoffs is hard. If you say there might be any kind of a risk at all, some people are going to get hung up on that or grossly overestimate those risks compared to the benefits (or to the risks of not getting the vaccine -- also not something everyone would be affected by but clearly a non-zero risk).
Taking that into account, "completely safe" might be a better approximation than most other ones you could make.
I think we are better of thinking of risk in terms of every day risk management. Comparing risks to things like driving 10 miles, getting hit by a meteor while sleeping, etc. can help create a better understanding of the risks.
Comparing to something else that people might have a more realistic intuition of sounds like a good idea.
Wind power is better for the environment - Similar to above, we don't really have data on the full lifecycle environmental costs of large scale wind farms. This is especially true because a good portion of the impact depends on how long the turbines last, what type of repair/recycle technologies are developed, and what type of policies get applied to recycling them. We see some things that look promising but others that are concerning.