1. Trend line doesn't fit very well (fails the eyeball test)
2. We don't see how many complaints occurred in pre-pandemic years, so it's hard to know the baseline comparison.
3. We don't know how the total number of sales compares by season. More candles may have been sold during months of complaint spikes; if we assume each candle has an equal probability of being defective, then an increase in sales will show an increase in complaints.
https://twitter.com/nick_beauchamp/status/147355576211076710...
For your point 1, this is a smoothed average. I suppose they should have used wider bins, but "failing the eyeball test" doesn't say much. The point isn't to fit the data, but to collate it so that you can clearly see the overall pattern.
There's the additional prior here that we know there were significant increases in COVID infection at the same time, which has a well-studied symptom of loss of taste and smell, that nicely correlates with these.